JJ's posted a bit about a role in our Platforms team, which is where I work. I thought I'd burble on for a little while on the sort of stuff we handle:

Platforms locally handle Windows itself, and most of the in-box and add-on technologies (like AD (inc GP), ADAM, ADS, CA, DNS, DHCP, FPS, RIS, WINS, IAS, RRAS, NLB, MSCS, TS + TSL, WM)  that come with it (excluding such notables as IIS, SMTP and Sharepoint, but we don't always shoot you for knowing something about it - more knowledge == better), plus various other platform-level products (SMS, MOM, ISA, Virtual Server, Virtual PC (Windows), IE). We do tend to specialize, so you're not expected to know everything about everything, just (some of everything) pretty well, and a little about the rest.

The job is primarily about troubleshooting. Lots of (quickly) learning how things (should) work, and why they sometimes don't. Lots of support from really, really smart and/or experienced people around you.

Some level of basic development skill can be a plus (AD scripting with VB or JS leaps to mind), but you most likely won't be asked to write any huge applications. Debugger skills are often useful. An understanding of Windows architecture at the big-picture level is mandatory, and the more detail you understand, the better.

So, if you have relatively broad and occasionally deep Windows skills, and are looking for a constant challenge, go check it out!