Horrible, please help

I downloaded something and was asked what program I wanted to use to open
it. I chose UTorrent, a download handling program and accidentally chose to
make it the default for all programs like the one I was dealing with. As it
turns out, I didn't really know what kind of program the one I was trying to
open was and now UTorrent is set to open many of my programs, including
Windows Media Center, Player, Live Messenger and others. Of course, none of
them work. I tried Start Menu>>Default Programs>>Set program access and
computer defaults, but that tries to open with UTorrent as well. I need to
know how to change these programs AND what program to change them to.