VirtualBox from an existing partition

"You can do this if you're using Microsoft's virtualization program, but I don't know that you can pack Windows into a .vdi file, but there is a way to run Windows as-is off of your physical partition:

http://dotneverland.blogspot.com/2008/08/running-your-physical-windows-xp.html

There's an old version of Dot Net Rocks that was all about running Virtual Machines. A lot of it is not relevant to your specific situation, but it's a good listen, and they talk about this type of migration (ie, the tools you'll need to run on the physical machine to migrate it, etc).

http://www.dotnetrocks.com/default.aspx?showNum=114"