I'd suggest investing in OS X 10.3 Panther along with the RAM. 10.3 will have a noticeable increase in speed compared to 10.1.5. It's only $69 through the education store.
FWIW, I've had great luck with crucial.com as well.
Duff-Man says...if you look in your utilities folder in your applications folder, you'll have something called Apple System Profiler (or System Profiler) - launch it and look through the info in the Hardware Overview section - it will tell you all you need to know....oh yeah!
Duff-Man says...glad to help....I guess it is a bit confusing sometimes when Apple changes the names on their utilities...took a while for people to get used to "Disk Utility" when 10.3 came out too....oh yeah!