iTunes 9 library can't find location of any songs...

Recently my family just upgraded our iMac Tiger to Snow Leopard, and purchased a second external drive with 1 TB space. I already have a storage drive that holds my music, movies, podcasts, photo documentation for art, etc. The 1 TB external drive was a surprise college gift to me, so my brother copied everything from the old drive to the new one. This was great, except somehow it screwed up the directory links of my entire library. I tried going to itunes > preferences > advanced > change location of media folder back to my original external drive because the music was still on there as well, but this didn't work. I tried defaulting to the original settings and music on the hard drive. This didn't work either. All of my music is still on the original external drive, so I tried locating the files one by one, but after fifty or so, iTunes got bogged down, and there's a ten second delay in between songs.

So. :/

Is there any way I can mass locate all of the songs without gutting my library?
I have just over 10,000 songs that I've put a lot of time and energy into organizing, tagging, etc. I reallyreallyreally don't want to lose all of that!

I would really appreciate some help!
Thank you!