If it's the Retail 10.6 Install Disc it can be installed over 10.4
Snow Leopard/10.6.x Requirements...
* Mac computer with an Intel processor
* 1GB of memory (I say 4GB at least, more if you can afford it)
* 5GB of available disk space (I say 30GB at least)
* DVD drive for installation
* Some features require a compatible Internet service provider; fees may apply.
* Some features require Apple’s MobileMe service; fees and terms apply.
Which apps work with Mac OS X 10.6?...
It looks like they do still have it:
And it's been reported that if you have a MobileMe account Apple will send one free.
If it's a core Duo & not a Core2Duo, then it'll only run in 32 bit mode.
I had planned to do a backup before upgrading to OS X 10.6 but my backup system has failed. I purchased a new drive and found that to use it requires at least OS X 10.5. How risky would it be to upgrade without backing up first or, would it be advisable to return the drive and purchase one that will work with OS X 10.4 currently in use and subsequent versions?
It is always best to have a full bootable backup before you upgrade. If you fail to do this you will be unable to return to this OS if you decide you don't like the new OS. Also there is a slight chance that an install could lose everything on the Mac. The backup must be to an external hard disk. Preferably use Carbon Copy Cloner to make a bootable backup of the whole disk.
Erase before the install
Once you have a bootable backup on an external disk it is best to erase the internal disk with the new installer DVD before you install.
During the install
Preferably do not import any data or preferences from earlier OSs during the install process as this can reintroduce bugs.
OS numbers and names
OS X 10.4.x - Tiger
OS X 10.5.x - Leopard
OS X 10.6.x - Snow Leopard
OS X 10.7.x - Lion
OS X 10.8.x - Mountain Lion
More about Macs
The Apple History site has specifications for every Mac ever produced: http://www.apple-history.com/
Upgrade to Leopard
Those wishing to upgrade to Leopard should be aware that install disks can be expensive unless you contact Apple. Details: http://lowendmac.com/deals/best-os-x-leopard-prices.html Standard Leopard installers impose several hardware limitations including speed and RAM size but all these restrictions can be overcome. Google for details. Leopard works well at 500 MHz with 1 GB of RAM and many happy users have less than this.
Upgrade beyond Leopard
OSs beyond OS X 10.5.8 require an Intel processor. If in doubt check this: Click the apple at the top left of your screen and select 'About this Mac'. This will give you your OS number. Then click 'More Info' to see which processor you have. If it says PowerPC you cannot upgrade to Snow Leopard and above. If you have an Intel Mac it is well worth upgrading to Snow Leopard now and then considering other options after that. You can buy Snow Leopard here: http://store.apple.com/us/product/MC573Z/A
Upgrade beyond Snow Leopard
Information about upgrading Snow Leopard to Lion or Mountain Lion: http://store.apple.com/us/product/MD256Z/A
Check that your Mac complies with any requirements. If you are not in the US you should use the Change Country link at the bottom of Apple pages.
The solid state drive that requires OS X 10.5 or above is being returned for a comparable one that can back up my OX X 10.4 Tiger system and higher upgrades. OS X 10.6 Snow Leopard has been received from Apple. Have checked out Carbon Copy Cloner on its website and will be downloading it for use with the new drive.
The clarity and completeness of your reply is really appreciated; especially since I like to be aware of all the details before proceeding.
Thank you Neville Hillyer. With the clarity of your step by step proceedure I can now plan to upgrade with confidence of success.
Began with a full bootable backup to a new external hard drive. Following your direction of July 11, 2012 resulted in the successful installation of Snow Leopard OS X 10.6.8. Then used Migration Assistant to transfer data. Initially it appeared that much data was lost in the transfer, including passwords in Keychain, until most applications were updated.
Just recently realized that Microsoft Office 2004 can no longer be opened or updated. But that's ok. I still have the Tiger backup on the external hard drive and am in the process of copying Microsoft Word documents into TextEdit and AppleWorks 6 for transfer.
After a lot of work, and some nail biting, The greatly improved performance and features of the upgraded applications made it very worthwhile. Thank you, for your knowledgeable direction which provided a pathway to avoid possible disaster.
My thanks, also, to BDAquawho provided the initial incentive to proceed.