I just did a quick scan of the page you linked to. They seem to be implying that .NET refers to the server end of the XP platform. In this case, there is no need to worry. I know for certain that 2000 MCSE's will not be required to upgrade to XP MCSE. The differences between 2000 and XP are minimal IMO.
I've had some experience with the .NET style of server... ISA 2000. All they seem to be doing is centralizing network services and making use of arrays and network load balancing. For example, ISA is a firewall, Proxy, VPN and pseudo Router. Any one of those components would be very familar to you if you are already familiar with it's 2000 equivalent. So, if you know Proxy, you know the Proxy component of ISA... don't sweat it, just stay up on things and you will be fine ; )