Many things this could be to be honest
First of all check the speed of your internet, if thats about what your paying for then dont worry about that.
speedtest.net
is the website for the test.
Secondly, what internet service provider are you with? I found out after being with tiscali for 3 monthes that there fair usage policy blocks and limits certain ports and speeds at certain times of the day. If you get me. So thats a possibility.
Thirdly, Limewire doesnt seem to work properly on my computers anyway, possibly router firewall? Internet service provider again (aol)? Windows firewalls?
If it doesnt work, could always use rapidshare, fast downloads but requires a premium account. Which are quite expensive.