Sorry I couldn't be more help. Although it seems a strange problem to be caused by the college firewall, it could be possible that they made a change which is causing you the trouble.
One last possibility which won't help too much unless you know the servers is with using specific ports to download from. I assume you can download from HTTP? Test with someone on port 1080. Have someone manually dcc a small text file to you on that port. Manual command is:
/dcc send 255.255.255.255:1080 filename
Replace the IP (255.255.255.255) with yours. And replace the filename with the file (use path if necessary). Also, if the path/filename has spaces, put quotes around the entire path\filename...
Example:
/dcc send 255.255.255.255:1080 "c:\program files\test.txt"
You can also try various other ports that are usually left alone by college firewalls... e-mail ports, for example.
You may also want to try different filetypes in case the college has just suddenly started blocking specific filetypes. That's one reason why I said to use a text file for the test.