You can set WMP to monitor your music folders and and it will add any new files automatically. Open WMP go to "File" > "Add to Library" > "By Monitoring Folders"> find your saved files folder from limewire, then click "add", then "ok".
You can find your saved folder in limewire, go to Tools>Options>Saving.
Sometimes you need to download codecs for WMP to play certain files. I've had good luck with
XP Codec Pack 1.3.0. Be sure to install it if you d/l it.
You may want to try another media player, as a backup if nothing else.
VLC media player is a good one that has the codecs built in and will play most file types.
More info here:
CODECs list and alternate players for Movies