This question looks a bit dated, but I'll answer anyway.
Answer: Complicated: yes. Simple: probably not necessary.
It really depends on what you need to do. If you need to use a feature not current supported by .NET, have-at-er. But be careful, most of the coddling the Framework provides Win32 does not, and if you do something incredibly stupid, your machine WILL bluescreen.
I know when .NET first came out, I had have no interest to learn Win32, .NET was here and it was such an improvement. But the sad fact about Windows is this: all new features in Windows are implemented in native code first, period. If you want to use any part of Windows before .NET wraps it, you're either using Win32 from C++ or Win32 from C# or from VB.NET. .NET is a wrapper, for all the stuff in Win32. So if you can't wait, yes, you can Interop into the lower bowels of the OS if you'd like.
Knowing Win32 and probably one day Win64 (whatever they happen to call it) will always be a useful skill. Any whizzbang technology requires underpinnings somewhere.