Using Vista, you'll need to look for your preferences folder in a different place. Try C:\Users\your username\AppData\Roaming\LimeWire
And more info about how to show hidden files & folders, and how to find the preferences folder here
LimeWire Pref Folder in Vista
You'll know if you've deleted the preferences folder properly...when you start LW, it will take you through the setup wizard. Also, all of the settings within LW's options will have reverted back to default. If you restart LW & don't have to go through the setup wizard, that means that you haven't deleted the preferences folder properly. In that case, make sure that LW's properly closed & start again!
Hope this Helps.