I'm guessing that your school has loads of blocks. I'm lucky enough to have the staff proxy with mine, the student one needed a login everytime (as do the Windows PCs there) and was quite a pain. Not being able to connect to Gtalk is unsurprising... all the ports for apps like that and MSN and such are blocked with the student proxy at my school.

Oh,you could try this proxy, it seems to be a pretty generic one that I've used to get pretty high up access with many different networks using proxies:

Proxy: 10.0.0.27
Port number: 3128