ITunes :: External Drive Crashed Where Music Was Stored?

Had everything conolsodated on an external drive which crashed. I have it stored on another system so I can easily get a new drive and put it on there. My questions are: I have around 200gbs of music, the extensions or whatnot are on the iMac drive, but the bulk of the music itself was on the crashed drive. I'd like to clean up the huge selection of songs when I copy to the new drive. So say I copy half of it to the new drive...obviously all the extra extensions and whatnot will still be on the iTunes on iMac.

Is there an easy way around this, meaning to get all the extra/old itunes extensions out of iTunes without wiping iTunes completely? Or will I have to manually delete all unwanted extensions and so forth? Also, maybe 100 sings were purchased through the iTunes Store (the rest was from years of CD collecting), those were on the crashed drive as well. I think I can, but want to double check...am I able to redownloaded those directly from the iTunes store? All software and such are up to date running Snow Leopard.