Depends upon which version of LimeWire you are using. See How to Share Folders (click on link)

My guess is the folder in question is @ C:\Documents and Settings\"your account name"\My Music. So it's just a matter of directing LW's Share browser to that location & selecting My Music folder.

On the other topic, do a computer search for mp3. Since WMP is a playlist player, it will add songs to its playlist no matter where the songs are actually located on the computer. So you may in fact have several locations where other music is located at.

Personally (I use a mac), I share multiple folders from my iTunes music library. Since iTunes organises its music library into artist -> album folders, this makes it easy to pick & choose which folders to share.