For VO, I'm using

Power Mac G5
Dual 2ghz (dual 1ghz bus)
1 Gig RAM
ATI Radeon 9600 Pro (64Megs)
Logitec RumblePad II
Apple 20" Cinema Display

I have also run VO once on a Power Mac Dual 450ghz G4 (also 1gig ram).

For a complete list of machines, go see:

http://homepage.mac.com/mouser/PhotoAlbum6.html

But only the above two plus the iMac were actually used for VO. The G5 mainly.

Power Mac
Dual 867mhz G4 (Mirrored Doors)
1 GB DDR RAM
Nvidia GeForce 4 Ti4600 128 MB VRAM
21" and 19" monitors
Wireless Microsoft (Gasp!) 5 button mouse
Split Keyboard
Various Speakers tangled and mangled together
Beatup highback leather office chair
Tolerant Girlfriend

Asus P3V4X Motherboard
PIII 800Mhz overclocked 30%
NVidia GE Force 2 MX 400 Overclocked 35%
Sound Blaster Audigy LS
512 MB PC 133
40Gb 7200 HD
17" ViewSonic A70
Logitech Z-640 5.1 speakers
Logitech wireless mouse/keyboard
Gravis Eliminator Precision Pro Joystick
...and oh yeah, am I the only one using the time tested
.... Win 98SE???