Firstly, what Wikipedia has to say on the subject:
And the virtual PC applications I have used, or rather, had closer experience of than the vast array of virtualisation software out there:
- Parallels Workstation
And finally, my personal opine on the subject:
- VirtualPC - Quite good, does what it says on the tin but hogs a lot of system resources. Will run non-Windows OS's, but probably is better running Windows. Discontinued, I understand, in deference to Hyper-V.
- Parallels - Not the same kind of virtual machine as VirtualPC, in that it's expressly designed to run Windows on a Mac, but it does this beautifully. It can startup Windows which has been installed into Parallels or BootCamp and run them side by side.
- BootCamp - Runs Windows on a Mac as a stand-alone OS, in that Mac OS X is not running at the same time. Allows the Mac to operate as a Windows PC and does it pretty much better than a regular PC can IMHO.
- VMWare - Basically just like VirtualPC, but many would have it as being more stable and not Microsoft.