Thanks. On 7/28 I saw a link (fastmac.com) on this site where I can buy an upgrade to 10.4 with free available upgrades to 10.4.11. I don't know if those "free" upgrades include the Combo Updater or not.
I am currently running OS X 10.3.9 on my iMac G5. It came with this operating system as well as 512MB of RAM and I had them add another 1000 of RAM when I bought it. I have lots of software that runs in Classic (for example, Photoshop 7) and I read that Leopard (OS X.5) will not support Classic...