Do you have Internet access, even though you cannot get into Windows Live?
Correct myself from above, they should be the same as Xbox Live (i.e. use TCP and UDP ports 3074 as well as TCP port 80), but also add UDP ports 2302and 2303 to open. Again, refer to the original link I gave above.For PC-based Halo 2, here's the link: http://support.microsoft.com/kb/829473
Please note these are different (except for port 80) for ports for Xbox 360 on Xbox Live (TCP and UDP ports 3074 and 53 should be open, and UDP 88 and TCP 80).