The Windows 7 roaming profile will be listed as user.name.v2 whereas the older XP profile will be listed as user.name (or however your usernames are setup).
The two profiles aren't compatible and won't roam to each O/S, so you'll have to maintain two I'm afraid. Same issue for me now that we've rolled out Windows 7 with users on Citrix and Win2K3 Server.
Lee