Thomas owns the MDA infrastructure, among other things, and has a great practical post about about how to deal with that annoying pinvoke MDA. Thomas worked on porting the CLR (especially the Debugging Services) to 64-bit and is the only one on the CLR debugger team (to my knowledge at least) that doesn't break a sweat when looking at ia64 assembly code. See his intro for more details.
Check out his blog here: http://blogs.msdn.com/tlai/default.aspx
(for some reason, I need to enter the 'default.aspx' part of the url).