Subclass NT to intercept SQL calls?

Is there a way that anyone knows how to intercept calls to a SQL server, and perform some extra authorization on that call?

The situation is this -- we have a hardcoded login/pw (don't ask - we bought this software, cause we had to) and it cannot be changed. We also have production, and a couple of developer servers.

I want to be able to examine the NT credentials of the caller, and either allow the call to pass thru to the SQL server, or deny it -- according to their NT group for access to Production or Test.

If you understand this - great - cause I don't know that I do myself, and all help or pointers are GREATLY appreciated...

Thanks all!

Peter