Can't share internet connection???

[hipopony66]

Ok, this should be an easy one for some of you here. I can't seem to get this to work. We have 3 computers at work all networked together to the computer in the server room. There are 3 server cases. I assume one is for backup, one is the mailserver, and the third is running Win 2000 Server. All the computers on the network are functioning just fine and are connected through the network. Here's the problem. The internet connection works fine on all the computers except one. They have a DSL connection here (on the computer running Win 2000 Server) and the other computers are sharing the DSL connection through LAN. It's only the computer downstairs that won't connect to the internet, so I'm trying to fix this for my boss. Normally when you load up IE on one of the computers, it connects you to the default homepage. However, on the computer downstairs I get the following message:

403 Forbidden- The ISA Server Denies The Specified (URL). (12202)

Internet Security & Acceleration Server

And yes, IE is the default browser on all the systems. Except for the computer running Win 2000 server, all the other systems are running Win XP. Any help with this dilema is extremely appreciated.

[Pc_Madness]

Make sure the computer downstairs is set up to connect to the internet through the Server?

[hipopony66]

how would I go about that?