Start with the basics before you get to the higher level stuff like web services (though that is important too). The most important things you need to learn, as a project manager, are the things you're going to be questioning your underlings about later. For example, my PM (also a PHP guy) has absolutely no knowledge of garbage collection and its implications, which makes it incredibly difficult for me to explain to him why our .NET Windows service appears to be taking 80MB of RAM.
Remember, you are not the one who needs to know everything. You should be issuing overarching directives, and let the people with the expertise sort out the details. That said, study up on the technicals a bit so that they can communicate effectively with you.
Edit (8/24/08):You should know something about the underlying technicals; not necessarily all .NET stuff either (garbage collection, .config files, pipes and services if you're running services adjacent to your project's main focus, stuff like that). Higher-reaching concepts would probably include WPF (maybe Silverlight as well), LINQ (or your ORM of choice), as well as the Vista bridge and related bridging code if your project includes desktop apps at all. Those three things seem to be the focus for this round of .NET. Something else that's very important to have at least a passing knowledge of is the ways that .NET code can/must interoperate with native code: P/Invoke, Runtime Callable Wrapping and COM Callable Wrapping. There are still a lot of native things that don't have a .NET equivalent.
As for resources, I'd highly recommend MSDN Magazine. They tend to preview upcoming technologies and tools well before average developers will ever see them.