Upon bootup there is a loading bar below the apple logo- TAKES AGES!

Does this computer have a BootCamp partition for Windows or another non-Mac OS?
If it does, that'd open up another area of probable cause; and possible cure.

If you have a decent backup of your work on an external drive device, you may need it.
Issues similar to yours occurred after an update or upgrade, in some instances noted.

You could try starting in Safeboot to see if that helps (does checks on startup) and that
is initiated by holding the Shift key down through the beginning of the startup sequence.
You would be asked to enter your admin password before the desktop appears. This
mode is de-activated by simply restarting the computer again... Also, check Console logs.

Sometimes, from what I can find using google, the gray loading bar can be a sign
of problems that may require using Time Machine or another backup (or a pre-made
clone, of the computer's hard disk drive content, before the issue) as a basis to re-install.

A cure may include the use of a third-party disk utility such as DiskWarrior, or maybe
Drive Genius, or TechTool Pro; suitable for Snow Leopard 10.6.7, and on a DVD.

Not sure where you were looking online for information, but there is a ton of situations
in Snow Leopard over the past few years with a similar symptom; and of them, a few
point to possible corruption or damage on the hard disk drive. Directory? Partition?

Does the use of the booted OS X 10.6 install disc, and running Disk Utility, verify,
tell you anything about the condition of the hard disk drive? If there are errors,
can the Disk Utility repair them? Aside from this, have you checked into the Log
files held by Console utility, to see what (if any) relate to the time of startup?

Some files won't get written into logs, on start-up. However, there is a self-test on
startup and the computer logs and System Profiler historically can tell if is passed.
Yet, the latitude there may be limited - to only say the computer did finally start.

When I googled the words: *Mac OS X 10.6: loading bar on startup* there were
60 thousand claimed results. While I doubt many directly apply to this issue, some
of the first 10 looked promising enough; at least when pointing to possible causes.

How full is the computer's hard disk drive? (as a percentage of the total capacity)
This can affect performance for both the OS X and installed applications. If that
were my computer, I'd already have checked a list of basics, over the past months.

Depending on variables, and information not mentioned so far, I'd consider checking
the hard disk drive using booted Disk Utility on install-restore disc; to look for errors.
Then, see if the Utility could repair them. And, would have a backup strategy in place.
(An externally enclosed self-powered hard disk drive, one that supports Clones.)

A free utility tool that can run routine maintenance, if used preventive, could help; not
sure now what else is happening. I use a version of Titanium's OnyX for my OS X.
But that can't help hard drive damage or directory issues.

If you are near an Apple Store with a Genius bar, call ahead and schedule an appointment.
Take along the computer's OS X software discs; if you have upgraded, take those too.
Be sure to describe this issue, and if you checked (verified) the hard disk drive, and choose
to go no further, that may tell a technician something.

If the computer has an extended AppleCare plan (three years service/support) calling there
would be a natural thing; at least to set a date on the record, and maybe get an incident #.
Should the issue later require a hardware cure, those matters are best addressed directly.

+This inquiry appeared in OS X 10.5 Leopard area; it may do better moved to SL 10.6 area.+

Good luck & happy computing! 🙂

+{ edited 2x }+

The use of Safe Boot mode should be ventured into with some familiarity; to
understand a little more about it. There are articles, documents, information...

(Actually, some of your Snow Leopard's slow starting is likely due to it's own
way of trying to negotiate past some issues it finds, in the boot process; so
that is why a +third-party disk utility+ may help, if a 'verify' of the hard drive by
use of your native OS X boot disc's version of Disk Utility can't fix problems.)

• Mac OS X: *What is Safe Boot*, Safe Mode?
+Safe Boot is a special way to start up when troubleshooting. Safe Mode is the state+
+Mac OS X is in after a Safe Boot. To perform a Safe Boot, hold the Shift key as your+
+Mac starts up. Starting up into Safe Mode does several things...+
http://support.apple.com/kb/ht1564

• Mac OS X: *Starting up* in Safe Mode (safeboot)
+Learn how to start up in Safe Mode.+
http://support.apple.com/kb/ht1455

• Safe Boot takes longer than normal startup:
http://support.apple.com/kb/TS1884?viewlocale=en_US

{Advanced tip: If you want to see the status of a Safe Boot as it progresses,
you can hold Shift-Command-V during start up (instead of just Shift).}

+Note: A Safe Boot takes longer than a typical start up because+
+it includes a disk check and other operations.+

There are other levels of access into the system, but without
some background or understanding of Terminal utility and a
grasp or feeling/experience in single-user boot, the methods
used by this process are best for GUI access for this task.
When a user can't get into a computer this way, is where
other methods of access are essential; or better tools and a
good backup clone on external boot-capable hard disk drive.

You can find Console in the utilities folder, by using GO in the
Finder menu bar, and choosing Utilities (folder) to open; then
launch Console. Several kinds of logs are reported here by
the running OS X system; those pertaining to the OS X and
all of the computer's basic running would be first to look into.

There are error logs, system logs, crash logs. See what the
system logs has, especially for date and time of the problem
where the computer takes forever to start. There may be no
log reports at all; if the system won't write them on startup.

A possibility in Directory issues contributing to this slow startup
or some damaged system startup files, exists. So, troubleshooting
may include checking the hard drive with the booted install disc's
version of Disk Utility, to see if it sees an issue, and then if it may
be able to repair the drive's issue. (not a permissions repair.)

This can be problematic, do not actually run the Installer on the
booted (hold C key on start with Install DVD in optical drive) disc
since the options and tools available there are to be found in a
menu bar and that is like a regular application window. When
done, the way to exit Disk Utility, is quit; To exit Installer, you
use the menu bar options to get and use Startup Manager; in
which you can choose to start the Mac from its hard disk drive.

If the Disk Utility can't repair a reported problem, then it may be
something to consider the purchase of a retail third-party disk
utility, such as those named. And they do require some learning
to know what they can do, and how to make them work.

The visit to an Apple genius, may be helpful. To have a complete
backup of your computer, (a clone; see Carbon copy cloner, etc)
you can restore or run/boot the computer from, is recommended.

You should check the computer to be sure it can start up in SafeBoot
and also not have peripherals attached to it, while troubleshooting.
They could contribute to symptoms, or be a cause of issues.

This article covers several symptoms on start up in OS X later than 10.3.9:

• Mac OS X: gray screen appears during startup
http://support.apple.com/kb/TS2570

There's so much more, but these may tend to distract from initial checking of
the basics. Perhaps a finer set of insights and help may be offered by another
reader who can sense this problem from first hand experience?

Good luck & happy computing! 🙂

+{ edited to add more, don't ask why }+