<p>What is the difference between Introspection and Reflection in .NET</p>

They're two parts of the same whole.
Introspection refers to the ability of a class to look 'inside' itself and see, for example, what parameters a method takes, what the names of its members are, etc.
Reflection is the specific name for how .NET implements introspection.  Other languages may call it something different (C++ calls its limited introspection RTTI, for run-time type information).