Gaming on a PPC G4... :D

Ok. so here's the deal. My lap (PC) broke down a couple of weeks ago and I had to switch back to an old PPC until I'll get a new one. Thing is that I've never really used Macs before and I know this thing is the "old generation" before Apple went with Intel.

I'll probably use thing for another month or so and I was wondering what is there available out there (exclusive for Mac or not, doesn't really matter) that is worth trying out just to kill some time...

I would also like to go back to some oldies that ran on PC (namely Thief series), but I know that I somehow need to do some tricks in order to make these older games run on a PPC I figured...

Here are the specs (quick relevant specs from the System Profiler):

Mac OS X 10.5.8
1.5Ghz PowerPC G4
2GB DDR SDRAM
Ati mobility Radeon 9700

Oh... and one more thing. This thing heats up incredibly fast! I only have Safari with a couple of tabs open and the fans go crazy. The underside feels incredibly hot to the touch.
Now I also know that Mac doesn't like flash much, but man! This PPC surely doesn't!!
I would also like to mention that the PPC is borrowed from some guy that was using it to gather some dust on a shelf. I don't want to kill it or anything, but I just feel so bad and a little worried that it heats up like that and I don't want to return it to him broken.