So...I've definitely decided I like VirtualBox the best. I am currently running Windows 7 Professional as my main OS, with a Xubuntu, Chromium OS, and Windows XP SP3 (32-bit) virtual machines. I use the Xubuntu box anytime I'm programming for my OS class (instead of having to deal with Cygwin in Windows). I use the WinXP box when I'm searching for anything dangerous (such as keygens, etc) since it's very difficult to get viruses through a virtual machine (however, you CAN get viruses, so still be careful). The ChromiumOS (Google's new OS that's still in like pre-Alpha) box I just installed to play around with it. It's pretty friggin cool!
Anyways, if anyone has any VBox questions, just ICQ me or PM me because I can probably tell ya what to do or what you're doing wrong. I think it's by far the best VM program out there and you can't beat free!!