- last post: 01.01.0001 12:00 AM PDT
I just dusted off an old PM 7500 (with a G3/333 card) and installed Panther on it to run Aquaduct. While I'm at it, I'm thinking of doing pretty much what you described: throwing the Marathon Trilogy and the OS 9 versions of Oni and the Myths on another OS 9 HD.
If that old thing can run OS X (albeit slow but fine for my purposes), the old Bungie titles should be just fine. I had used it originally back in college and was playing Marathon 1-Inf over the LAN without too much problem... with the original 601 in there. Then again, I'm used to snappier things and highr frame rates now.
Your best bet would be a smurf G3, I'd think. They can be found a little easier than the older PowerMacs and are about as cheap (under $100 for a barebones one). Also, they can run a few other things if pressed (like be a file, web or backup server, for example) without needing to upgrade too much. A G3/anything would run the Trilogy in 9 smooth as silk. Upgrades if you need to, like hard drives and RAM, are more standard and also easier to find cheap (PC100 and IDE vs. FPM DIMMs and narrow SCSI on older PowerMacs).
If that's too much, try to find one of the older ones even cheaper as the previous poster(s) suggested. You may need to get more RAM and, maybe, a processor card if it seems sluggish, though.