Here are some possibilities:

Do you have your iTunes music folder set as your Shared Folder?

Do they all have the .mp3 extension?

Have you moved any folders around recently?

LimeWire "hashes" your files. This can take some time. If you don't leave it running long enough to finish, all of them won't show up until the program is on long enough to complete them all. And, if you move the folder(s) around it does them all over again.