I have the same problem, but only since I switched ISP to Toucan. Now, I can only get Limewire to download stuff during "off peak" hours, i.e at weekends, or during office hours in the day. There is nothing that can be done about it apparently. I suggest you try out different times of going on, such as during the daytime, or after 11pm. It's not just Limewire, Kazaa and Ares are the same also.
Hope thats of some use. Not ideal I know, but at least if you know times that you are able to download stuff, you can work things out accordingly.