Peer-to-Peer Win2k & WinXP

I had two Win2K machines networked (Peer-to-Peer) and each was able to connect to a DSL ISP. One of the machines died and I replaced it with a WinXP box. The connectivity to the DSL ISP works OK but I cannot get the two to recognize eachother in a Peer-to-Peer topology. WinXP will not accept such a topology, this is my first taste of WinXP, what has changed?