Constant Freezing

I'm (trying) to run OS X 10.4 on an old PowerMac G4. However, it will randomly freeze when I try to open programs or hide/show the dock, or anything. I only have 256 MB of RAM in there. My first thought was that this OS takes up too much space in memory if I have several programs open. Any thought on what the culprit is? Any way I can make OS X less "demanding"?

According to Apple, 256 MB RAM is the bare minimum to run OS X 10.4 on a system.
A more reasonable minimum would be 512 MB RAM, especially if you are running on an older system. If you work with mulitple applications, your best bet is to upgrade your RAM.

And, even if a stick doesn't say "compatible with Mac", if it's the exact same memory type, it'll work right? There is no Mac specific memory right? (sorry, new Mac user...)

Cool, I had an old broken Sony VAIO with the same type of memory. Now I have 768MB of memory! No freezing now.