I use VirtualBox on Mac OS X with an XP guest OS. Works perfectly, and the install was painless. I use it for my ‘have to have’ Windows applications. I set it up with Mac OS connected via Wifi to one network and WinXP connected via cable to another network (I work in a school and there is a student network and a professor network). It's great and then I can access all my applications on all networks at the same time! BTW, I found it really easy to install and setup on Mac OS X, Windows and Linux actually (debian)! »