I run Debian in VirtualPC and use XDarwin to display graphics. This allows me to run wine which is often better than running Win98 in VirtualPC.
VPC in OS X is definitely slow however, probably because they are using the old event manager code instead of Carbon events. I think I'll try to get my old Dual PII running, I think the emulated 10BT card is a bottleneck and using my 100BT LAN will actually be faster.