Before buying anything you should first make sure your machine will accept the upgrade you have in mind.
Minimum specs for Snow Leopard. Mac OS X v10.6 Snow Leopard -Read the Technical Specifications
From the USA go to http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard
In Europe or otherwise substitute your national code in place of /us above.
In the UK … the last known price was £14.
Before you start upgrading, back up your files.
Once you have upgraded to Snow Leopard you will need to apply the Combo updater. Mac OS X 10.6.8 Update Combo v1.1 and follow with a software update to pick up any later security updates.
Thank you for the information Seventy one, I really do appreciate it, BUT I can not upgrade anything until I can find an upgrade to OS X 10.5 from my current OS X 10.4.11 :-/
You can go to Snow Leopard directly from Tiger, you don't need Leopard first.
Unless Leopard and not Snow Leopard is what you actually want!