Automator to sync iTunes Libraries

I recently bought a 32gb iPod touch, an upgrade from my 2nd gen 8gb. I love all kinds of music, and now I have room for much more. On my family computer, everyone has separate accounts and iTunes libraries. What I would like to do is get all of their music onto my account, then create a Folder Action that will put any music they add into my library too. I think I will be able to create the folder action relatively easily. But here's what I would like help with:

An Automator application that will compare another account's iTunes library with mine. If it finds music on the other account (that I do not have already), then it will add it to my library. I do not want it to add music that I have to the other account.

If it matters, I have Snow Leopard.

Thanks in advance!

 

Also, how do you check a folder AND all of its subfolders using Automator?