where did files i received in mp3 realm go?

Probably to the downloads realm.

Go to the Tools menu on the menubar, then click Received Files...

Vista moves downloads to a different folder without telling you if your download folder is in the mIRC folder. It's in a Virtual Store folder in the Applications Data folder under your login name in Documents & Settings. I forget the actual path, but a search on this forum for "Virtual Store" will give you the answer. In any case, you can just change your download folder to anywhere outside of the Program Files folder and you won't have any problems.