10.4.11? Whew, that's old stuff. It's hard to say whether it's something with your hardware, your software, or both, given that both are pretty old. I'd suggest upgrading to OS X 10.5, which will have received newer graphics updates and frameworks than 10.4.11 (which has been out of support for some time now, if I remember correctly). As you're probably aware, you can't upgrade to 10.6 because you are on a Power PC processor, while 10.6 is Intel-only, but I can vouch for the fact that 10.6 has no issues with it.
10.5 is a worthwhile upgrade over 10.4. Trust me, I've used OS X regularly since 10.3, and dabbled in it since 10.2... it's all come a long way.