tandem proxies

Hi,
My university requires that I use a proxy to get past the firewall to
access the internet; however, I need to connect to another computer
outside the university to access journals etc--the latter proxy
requires authentication while the former does not.

Currently, the way I have setup is to export a shell variable called
HTTP_PROXY; and in the firefox connection preferences I use the
"automatic proxy setting". This allows me to get out the university and

use the internet but I do not know how to use the proxy on the second
computer simultaneously using the first proxy.

Suppose the ipaddress for my school is ip1 and port is p1 and the
ipaddress to a machine outside the school is ip2 and port is p2, with
username user2 and password pass2.

How can I set it up so that I can use these proxies in tandem (i.e. use
the school proxy ip11 to get out of school and then use ip22 to
connect to another machine to access journals). I am on fedora code 5.
many thanks
les