I have a Nokia 5800 with Garmin Mobile XT and managed to transfer recorded track to the PC as follows:
1. On the Mobile XT > manage my data > tracks > save current track
2. On the Mobile XT > manage my data > manage > export GPX
(Now, the file garmin/gpx/current.gpx is updated.
3. connect the Nokia to the PC in mass storage mode, without running Mobile XT.
4. start mapsource
5. in mapsource, file > open and choose to open a gpx file.
6 navigate to open the file garmin/gpx/current.gpx
Now the track is in mapsource.
Hope that it helps.