Virtualization?

Hello. I was wondering if anyone knew of any open source or freeware virtualization programs for ANY windows platform 98se or higher. (an x86 emulator to be precise.) bochs is too slow and i want something to run off a portable usb2 harddrive. any suggestions would be welcome, and if its not possible at this time, no big deal. i work with many different OS's in my classes, and this would be very helpful for homework, and when i cant get lab time while at school, (just hit the open lab (WinXP only, or the library[also winxp only]). Thanks for any help.