I can't seem to disconnect (as in File - Disconnect) whenever I am connected to the net! Help! (Sometimes it's nice to just listen to the music in my library and not use up bandwidth downloading)

When you disconnect from the network, you don't disconnect from the people, that you are already connected to and up/downloading to/from. You have to kill/pause those, if you want your Limewire running but not using bandwidth.

Alternatively you can close limewire and then restart it, then press disconnect right away. Or go to Tools-->Options-->Connections and remove the checkmark from 'Connect On Startup' (Note: you will have to go to File-->Connect everytime you want to connect if you do this)