Microsoft is already hard at work on improving security even more in Long-horn server and the next generations of Windows. Some of the changes include:
Improved IPv6 stack and support
RDP over HTTP (don't confuse with RPC over HTTP)
Application IDs (uniquely identifying the integrity of registry vendor code)
Read-only domain controllers (BDCs anyone?)
A much anticipated future security feature is something called Server Core. Server Core will be a supremely stripped down, locked down version of server editions of Windows. It will contain no GUI, and function solely as an infrastructure server. The roles it will play include file server, print server, domain controller, DHCP server, and DNS server. It will be high performance and high security.