If you can get out with a browser, without having to use username and password, then seti can get out.
We have a firewall at my work too, but since seti uses port 80, there is no problem.
It's mostly with proxy it's a problem.
If this is your case, try setting IE's LAN connection to use your proxy.
If I use that way seti most of the time will be able to get out
Hope you get it to work
