Limewire is NOT built for speed and never was. Also, keep in mind it doesnt matter how fast your connection is but what the host is allowing for bandwidth and if that host is sharing, you may see 10 but that doesnt mean 10 hosts are allowing you to download at the sametime. Most hosts tend to turn of their bandwidth, making you downloads go even slower than normal. Have you configured your firewall settings?

edited to add: what version of Limewire are you using and where did you download it from? what OS are you using?