My gut feel is that it is a DNS problem. That is the system that translates URLs into IP addresses. You must have a valid DNS Server address for the PPC. Normally that is provided by whatever is providing the PPC IP address, and that is done automatically via DHCP, by the router/Access Point. A way to tell what addresses are valid is to run ipconfig /all from the command prompt on your desktop. On the PPC similar info can be had be using vxUtil or vxIPConfig, both free from
www.cam.com.
I haven't specifically tried it, but I would not be surprised if MSNM worked without a DNS entry, since it is a single use, proprietary program that may not require a lookup to find MSN IM servers. Regular sites, though definately need a way to look up the address from the URL. Another way to implicate DNS problems is to try going to a site by IP. Try
http://207.218.248.21/ in the address window. If it gets there it is a DNS resolution problem.