Is this the first version of LW that you've had on the Vista computer?

Just try deleting LW's preferences folder - it might not help but then it might
Check here for instructions: LimeWire Pref Folder in Vista
The main thing to remember is that LW has to be completely closed before you delete the folder - otherwise it won't have any effect.

If you haven't tried LW 4 with Vista, install 4.18.8 & see whether you still have the same problem. You can download 4.18.8 from your Pro download page - there's a link on the left hand side 'get LW Pro classic'.