For convenience and to stop having to restart the iMac to get into Windows XP, I needed Parallels Desktop for Mac. This is a very smart piece of software. The retail box came with an old v3.0 build but you can just download and install the latest build - build 5582 at time of writing. Use the activation code from the boxed copy.
Considering what the program achieves in terms of emulating Windows XP within OS X and the complexities that must involve, the install pretty much sailed through (a bit surprising considering the horror stories in places like MacNN Forums). I chose to use the existing Boot Camp version of XP which it spotted and updated with its own drivers. XP needed activation again after installing, and then again after I'd rerun the Boot Camp version and gone back to Parallels. The last one was via the Microsoft automated telephone activation. Fortunately that did the trick - breathed sigh of relief.
The verdict - so its a bit slower in OS X but entirely usable, very well thought out and very convenient for quickly checking something under XP or running an XP only program. I discovered the drag and drop by accident, moving a file to the XP desktop rather than Mac wastebasket - fortunately it wasn't anything large like a DVD ;-)