If that combo (same Mapsource version?) works fine on XP, it sounds like it's probably an issue with Mapsource and Win7. How large are the map tiles for that mapset? There's some peculiarity setting off the troubles. Have you tried other mapsets?
I don't have Win7, but I do have two machines with two different Vista installs. The TX topos (gpsfiledepot sourced) work fine on my machine running 64bit Vista Home Prem.
I don't have Win7, but I do have two machines with two different Vista installs. The TX topos (gpsfiledepot sourced) work fine on my machine running 64bit Vista Home Prem.