problem with yahoo

[kumar_ldh]

I dont know if it is an issue with wingate or yahoo. First my Lan Config
6 PCs all on Win98SE with IPs from 192.168.1.1 -192.168.1.6 connected through a 10/100 Hub
We have a Cable connection on one machine where WinGate is installed.
Server also has Norton Antivirus 2003 and it is enabled.
The problem is that We can't use Yahoo! Msngr on 4 machines out of 6. It is asking for Proxy server settings and I have changed and tried every thing, but still the problem is there. On one machine we are unable to logon to yahoo chat/mail/any Yahoo! web app.
I emailed Yahoo! and they say it is Proxy server problem.
Iterseting Point is that We can logon Yahoo! using Trillion and also we r able to do web browsing on all 6 Pcs. I can also connect MSN Msngr which needs a port at 1861 to be opened at proxy server. I had not opened any port for MSN.
What can be the problem.