If your user account is an Admin account, there may be an issue;
however if you see the missing items still in their expected location
(not their Dock links, but the real items in Applications folder) then
you may want to see if your account is correctly set up.
You could make a second user account as a test. By default, most
items would appear on the Dock if you had an original install version
OSX that came with the computer. Much less if you only used the
retail DVD, as that does not include iLife, iWork, etc.
Was the OS X installed when you got the computer? You may have
to see what kinds of installation discs and content is available to you
that could work in that computer and consider a complete reinstall.
If you did not get the install-restore DVDs for the OS X system or
the original system discs for the computer (OEM parts) you could
contact Apple Support or ApplecCare by phone, with Serial Number
of your computer handy, and ask if you can get a Replacement
Install disc for OS X 10.5 (or 10.4) so you can re-install completely.
This topic has been covered a few times, in ASC discussions. If
you need system discs, they should match the build year model
and if restore discs are not available, the replacement disc may be.
These will cost a modest fee from Apple. Much more if you look
into the retail or ebay/amazon resellers. Other sourced discs may
not match the hardware you have. Be wary of gray lable installers.
Also, there may be low-level or sector damage on the hard disk drive
if the system acts messed up, so a thorough erase/install process
could be used; as part of a troubleshooting effort. The hard drive may
be going bad, if the system starts missing parts, acts up, crashes.
Wear items such as hard drive, optical drive, and other parts can
start to show up when issues present themselves in an older Mac
or any brand of hardware. Troubleshooting helps tell if the problem
is based in software or hardware. Techniques vary to find this out.
Hopefully this helps...
Good luck & happy computing! 🙂