Astute developer Albertas Agejevas realized that Virtual Earth uses tiles similar to Google Maps, and he was gracious enough to contribute a patch that allowed Maemo Mapper to work with Virtual Earth maps.

Maemo Mapper v1.3.5 adds that patch into an official release. It also fixes a route auto-update bug and adds the ability to specify your own route download server.

The Maemo Mapper v1.3.x thread (post #2) contains the URL formats that you would need, but for quick reference, these are the URL formats (use at your own risk; I cannot be held responsible for anyone's use of these URL formats):

Virtual Earth (street)
http://r0.ortho.tiles.virtualearth.n.../r%0s.png?g=45 (link to copy/paste)

Virtual Earth (satellite)
http://a0.ortho.tiles.virtualearth.n...a%0s.jpeg?g=50 (link to copy/paste)

Virtual Earth (hybrid)
http://h0.ortho.tiles.virtualearth.n...h%0s.jpeg?g=50 (link to copy/paste)

Just copy/paste any of these URL formats into Maemo Mapper for access to Virtual Earth maps.