been there, done that.
I just spent a week trying to write instrucitons and figuring out how to do the 2007 restore.
(I do SG's not mailboxes).
1) my first problem was that there was some security issue in that I was not given access as an admin to exchange 2007. ( I am a unix person, as well as the backup person) I had to ask the windows guys to figure out what was wrong. But am not sure what it was.
2) this issue was obvious when I went to do the restore and the field was grayed out telling where to put the log files.
3) someone else had made the RSG and I could not get it to work. So I deleted it and make the RSG myself. This seemed to make a difference.
4) I was told that you should do the restore from the Backup Arachive and Restore window on the exchange server. Not sure why but I was told this works better. But don't open it prior to makeing the RSG. Again don't know why but I made the RSG after I opened it and I still did not have the access I needed. Close it and opened it again and it worked.
I am now able to do restores to the RSG just fine.
Only issue is that you cannot run Exmerge on a 2007 server.
but if you still have it on a 2003 server you can run it from there and choose the 2007 RSG to get your mail box.
We are still trying to work out the instructions for extracting to a pst just one mail box instead of having to do a merge.