This may or may not make a difference but try deleting your LW Preferences folder whilst LW is closed; instructions here: Point #2 & 3 in Fixes for Limewire (sample image included at bottom of page.) Make a note of any important settings because once you delete the LW prefs folder, you'll need to reset all your options once you re-open LW!

BTW is your speedtouch a USB connection?

Recheck Norton: Configuring Norton Internet Security

One thing you can try after this is go to LW's menu bar, Tools>Options>Advanced>Firewalls & change the Listening port to one between 49152 - 65535 such as 64049 for example.

Edit: I did notice them mentioned here http://www.kitz.co.uk/adsl/caps.htm because the offer specific plans of total allowable downlds per month. It doesn't say what they do if you pass the limit.