I haven't heard of anybody else using a http proxy. I know not how! Sorry. Have you tried the other types of proxy? Remember that the port no. you put into the proxy setting for LW must also be the same for the listening port. eg: port 3380 for proxy then port 3380 for listening port.
Connecting from a school is always a tough call nowadays.
I presume you saw:
A Fix for those whose ISP's block Limewire pages 1 & 2 which has a link to alternative instructions. ANd also the xtra images I posted here:
http://www.gnutellaforums.com/showth...threadid=35324