The BCL team has been blogging recently about long file path support in the .NET Framework (or lack thereof).  Their most recent post provides code samples for p/invoking to Win32's CreateFile, DeleteFile, FindFirstFile, and FindNextFile.  If you're looking for additional examples, we've run several related articles in MSDN Magazine.  For example, the .NET Matters column in our December 2005 issue provided a .NET interator based on FindFirstFile and FindNextFile, and the .NET Matters column in our January 2006 issue provided an example for accessing NTFS streams from .NET, which necessitates p/invoking to CreateFile in order to avoid the path format checks.

-Stephen