Music killing computer?

Hey,

We have a Dell Computer with Windows Vista and a MacBook Air. Our Dell is slowing down to the point of almost crashing many times a day because we have all of our iTunes purchases/imports on it. We have 3,400 songs, a little over 23 GB, and about 36 GB total with TV shows, movies, and other things. I tried transferring all of the music over to the MacBook Air, and it kept freezing. Then, I figured out that it froze because there isn't enough space on the MacBook Air to hold the music. I put everything in our library onto our 64 GB iPad, and tried to transfer it over to the MacBook Air, and it only transferred the purchases, and not the songs that we've imported. I'm not too savvy when it comes to this kind of stuff, and the only other solution I can think of is putting everything we have on DropBox until we figure out what to do. Still, though, we would prefer to get all of our songs/movies/shows/etc. off of the desktop computer because it is slowly destroying it.

Thanks for any suggestions on what to do!

Mark