Windows 2008 - a look at Server Core
I've played with the 2008 betas -- pretty sweet -- but I hadn't bothered to play with Server Core specifically.
Until I can run ASP.NET on Server Core, I probably won't bother. And even then, I suspect it will never be much more than a VM on my fullblown 2008 machine.
Now if only I could get a copy of SP1 for my Vista machines that is guaranteed to NOT brick my notebooks.