I assume you mean to recover your data from the XP machine to the Vista machine. Pitfalls would be user account control. If the account on which your XP data was written was set to keep files private, then in order to read them on VISTA you will have to go into the Control Panel, User Accounts, and turn off User Account Control. This would be true as well if you have to use the recovery tool I mentioned, but thats a simple change to make and when you are done, you just turn User Account Control back on. The conflict comes because the user account you are using to access the drive is not the one that wrote the files. But not all XP accounts are set this way.
Hope this helps. Let me know if you need more information.