I just read an interesting article about Windows 7 - it will include a virtual machine to run windows XP for backwards compatibility.

http://www.computerworld.com/action/article.do?command=viewArticleBasic&...

The article points out that this has the drawback of extra maintenance.

I'd have to agree with this - it's one of the big downsides of using virtual machines for testing -  with three virtual Windows' I find myslef constantly having to run updates.

One of the big wins of Linux systems is centralised updates for all applications - having to update windows, office, flash, firefox, java - all separately is a real pain even when you only have one machine to look after.