Problem: opening files from Explorer forces new VStudio instance

I hope someone can help with this, because it's making me crazy.  I've
done quite a bit of searching online and can't find the solution.

I recently had my XP profile become corrupt.  I rebuilt the profile in
the usual fashion, but of course some things are lost.  The particular
problem I need help with here is that now when I go to Windows Explorer
and double-click a file that is registered to Visual Studio 2003, such
as a *.vb or *.config file, it opens each file in a new instance of
Visual Studio.  What it used to do was open these files in the
Miscellaneous Files folder inside the running copy of Visual Studio.

Does anyone know how I can restore the old behavior?  Help!