Connecting to internet behind an ISA server, can browse cannt chat, updates

[true_friend]

I am an ubuntu user. using cable net. my provider is using ISAserver on his machine. on xp ( i have dual boot) my internet is working well but on linux i could not connect to internet. now through a script (http://www.linux.com/howtos/Web-Browsing-Behind-ISA-Server-HOWTO.shtml) i can browse the internet but i can not fetch updates and connect my messenger (gaim) to internet. can some one tell me its solution??
i also tried altering proxy settings but did not worked at all.
Regards
True_Friend

[je_fro]

What a hassle. I'd ditch that ISP immediately and get a better one.

[true_friend]

u are right but here at this time no better isp is available. may be in future.