I am concerned that you cannot find any of the titles or artists by using Finder. This would suggest a number of possibilities, eg either that Limewire has not actually saved any of the downloads to your hard disk or that you have a hard disk problem of some form. However, we'll start with the least serious possibility. When did you last do an archive? Finder relies on the current index by content to "find" the target text. If your last archive was performed before the downloads, Finder will not "find" them.

If you open Preferences in Limewire you should see which folder is nominated for saving — it should look like /users/yourcomputer'sname/shared/. If there is no folder nominated for saving, use the default setting. That should give you a more obvious target for future downloads while you wait for the indexing to be completed. If a folder is nominated, open it and you should find you MP3s inside it.

Report back if Finder fails after indexing by content and I'll go to the next step.