I am running 10.1.5 on an 8600/300 and have to say it is pretty decent on performance. I would recommend you get yourself a cheap PCI Radeon or something of that level which will give you some supported 2D/3D acceleration under OS X for it to be truly bearable, along with a good half-gig of RAM. (The ATi Mach chipset isn't supported since it is so freaking old... I have seen P133s with those things BUILT IN)
The first-gen Radeons should be cheap, and you can get 128MB DIMMs for the PowerSurge models for about 25$ a pop from OWC, which is the best price I have ever seen for FPM DIMMs, and the RAM works (I have 2 in my machine right now).
Once XPostFacto can support Jaguar (sometime after Jaguar's release), then it will probably be really cool. I have had a shot to play with Jaguar on an iBook, and other than some odd behavior with the Finder (it is constantly crashing at times), it was pretty slick, looked good, and performed well. I don't care what people complain about, but the dropshadow on the cursor isn't CPU intensive, and gives it a slightly better look to it. I liked the dropshadow in Win2k, although Jag's cursor shadow is a little better since it isn't so obvious.
