Ok I tried theunlockr.com cause .net wasn't working for me but i couldn't find anything on rolling back to 1.5 but if I find anything I will post a link here
See this post (plus read up a few posts to get some instructions.)
If you installed one of the leaked ROMs, you cannot go back down to 1.5. If you were upgraded with the over the air update, you are able to go back to 1.5. (Of course, you should be nagged to update to 2.1 from the start.)