This is just a short note to share my witness on the fact that VirtualBox on MacOSx works just alright. I quite regret I paid an extra for Parallels when I bought my Macbook Pro. As time went I had to uninstall or disable all of the whistles that Parallels had (like coherence and application shortcuts) as they were eating the battery, disabling the sleep and all the other stuff. And every time I had to investigate who and why, while getting only happy marketing emails from them. Never – “we found a problem because of OSX.XYZ update, please react/upgrade …”.
Never mind, I hope my note will help you if you are picking the VM platform for your mac. Give VirtualBox at least a try, its painless, free, can pickup almost any hd format (except for parallels of course, but you can convert …) and runs on almost any OS platform you can think of.
Converting parallels hd: http://benfrain.com/notepad/2009/03/osx-converting-parallels-or-vmware-to.html (be sure to read comments as well if you are converting). Myself I just used the winxp vm I had for ages running under MS VM.