How To Debug/Analyze DLL Access Violations

I have a application that I created a DLL for Outlook.  I have several
customers that is reporting that the DLL "crashed".  I have no idea on
how I can debug the DLL.  One customer reported that is causing her
Windows 9x machine to crash (BSOD) which I doubt it has nothing to do
with my DLL but, she's insisting that it is.

For a C/C++ project that I have used in the past I request the user to
send me a user.dmp file and I use that to analyze the crash and fix
the bug or find the cause of it.