Wowsers!
The new beta of Parallels is just, um, amazing. It can mount a Boot Camp partition and let me virtually work in Windows (XP Home SP2) without needing to reboot!
The only downside to all of this is that you cannot "Pause" the virtual machine, but booting takes mere seconds on the i(ntel)Mac and the ability to drag and drop and copy files easily from OS X to the virtual XP box is a HUGE time saver.
This tool eliminates the need to have separate computers for OS X, Linux, XP, Solaris, etc. Simply virtualize and go!
This is definitely going on my list of handy to have tools. As a total tangent it runs Solaris 10 (x86) Update 3 perfectly well.
I would recommend you max out the RAM in your system before you start seriously using virtualization otherwise you may find your harddrive churning and slowing things down significantly.