I'm about to catch my flight for the PDC, but I wanted to archive the following before I go:

In one of our session's demos on Tuesday, I'll be briefly mentioning C# code that determines whether a given file is a managed or unmanaged binary by inspecting its PE header.  Here is the C++ code it's based on, in case you want to check it out.  (Look for the part of the page that says, "Is there any way to find out if a given DLL is managed or unmanaged without trying to load it?")