Ok, I already have a me.com account. I made it when I got my mac a few months ago. I just logged into the appleID management site applied.apple.com using my me.com address as my appleID as you specified and it works!
HOWEVER, under "AppleID and Primary Email Address" it has my hotmail address listed and when I change it to the me.com email address, underneath in red appears "You cannot create an Apple ID using a MobileMe account. If this is your email address, it is also your Apple ID."