There is potentially differences in the way objects are recognized between XP and W7.
There certainly will be performance issues and different lengths of wait between the two machines. So it depends on how robust your delay timings are. If you have used dynamic waits then you should be ok.
W7 probably uses a different IE than XP unless you updated the XP version.
There are changes in the registry for 64 bit.
There may be a plug in needed for W7 for QTP 10?
The program files path might change
The documents and setting folder path will change.
To sum up there are differences between XP and W7 64bit that will need to be addressed in your scripts.