Both your problems could be ISP related. Your ISP's might be filtering LW's bandwidth.
Jord I suspect you're probably in this boat because an ip check suggests you're using a well known ISP in UK that does not like p2p sharing programs. If you can tell us your ISP name I can direct you to more specific ideas & what to do's if possible.

emmtee try downloading a magnet link from here & tell us what happens re: connecting to the file & speeds, etc. http://www.magnetmix.com/video.shtml
If poor result, then try deleting your LW Preferences folder whilst LW is closed; LW prefs folder is found here /Users/your_username/Library/Preferences/LimeWire

Make a note of important LW settings however because after you delete the LW prefs, you will need to reset everything once you restart LW.