I have to try this: 

VentureCake » Blog Archive » 10 minutes to run every Windows app on your Ubuntu desktop

It uses VMWare, SeamlessRDP, and rdesktop to run Windows apps from a virtual machine, and display them on your GNOME desktop.

VentureCake also has a helpful guide on running an existing Windows installation from Linux by setting up VMWare to use Windows from the physical disk (rather than a virtual image).