I would definitely recommend PIII 600. 450 would be ok for a single Voodoo 2. I'm running my PIII 1Ghz downclocked to 750Mhz due to 100Mhz bus - this is also an option for you.
There is also Coppermine Celeron 1Ghz with 100Mhz FSB. There were 800 and 900Mhz versions too. Another option is to buy Coppermine Celeron 566-633 (66 FSB) and overclock it to 100Mhz FSB. If you buy a few of them (they are very cheap, nobody buys Celerons) there is very good chance they will run at 850-950Mhz if your board allows setting 1.75V voltage (standard for 1Ghz PIII).
Pentium III 900E, ECS P6BXT-A+, 384MB RAM, NVIDIA GeForce FX 5600 128MB, Voodoo 2 12MB, 80GB HDD, Yamaha SM718 ISA, 19" AOC 9GlrA
Athlon 64 3400+, MSI K8T Neo V, 1GB RAM, NVIDIA GeForce 7600GT 512MB, 250GB HDD, Sound Blaster Audigy 2 ZS