I am not knowledgable about using proxies. But do know many schools nowadays have special anti-p2p program filters/blockers or shapers.

When you are trying to connect, go to the Connections window of LW & see if any ultrapeers are connected to at all. If there is at least one that is connected to without continually trying to connect to them then that is good news. If nothing appears in that window then that means you are not reaching the gnutella network at all. And either the proxy isn't set up properly or you are being blocked by other means.

Are you able to choose your proxy number? AFAIK when using proxies, some numbers don't work or don't work well, so trying out new proxy numbers until you find one that works. This may or may not be of any help but have a browse thru this thread: A Fix for those whose ISP's block Limewire pages 1 - 3 which have links to alternative instructions.

How do you have it set up at the moment with the proxy & the LW proxy settings? What type of proxy is it?