Considering lower price of hardware these days especially RAM you can easily go with vmware. Here is my system configuration
Celeron 1.7 GHZ
Windows XP SP2
512+256MB RAM
20 GB IDE ATA 100 HDD
845 Chipset board
I run vmware under XP and runs at least 3 os at a time
OBSD 3.6
FBSD 4.10...