There is Microsoft VM, but I have been buggering about with virtualbox.org for the last couple of days.
I am impressed but while it is easy to set up, it does take a bit to sort out the niggly nagglies.
Really I just wanted a dual boot Ubuntu to mess with.
Made a Live USB, was happy, then installed it.
I don't like the bootloader screen. Want to keep my own. So took me an evening to get rid of it (in spite of backup images). Palava.
Then tried Jolicloud. Didnt like it, but at least it can just be installed from Control Panel (I am W7 64 Home Premium btw)
But it did get me thinking, dont want to reboot to another OS just to do something...so Virtualbox came to fore again.
Only hassle with setup is a bit of lateral thinking with ISOs, shared folders and USB, CD/DVD devices.
Otherwise it comes up with "media not found machine halted"
(try a Reset instead of start new. Right click all Settings and investigate)
I had Ubuntu up and running in half an hour, XP in an hour)
The check boxes mentioned in the above guide don't seem present on my vbox download, but you can find ways to enable via tabs. Just took me a while to suss out.
I still havent had time to find my many partitions and my external drive.
But can see my CD/DVD, so in worst case I can write to a CD/DVD RW and get stuff in that way till I sort it out completely.