I had the same problem but didn't get much response from the group and didn't have time to fiddle with it. It was a one-shot, so I just exported text from Access and imported the text into SQL Server. I've also had success exporting from Access into an SQL database using ODBC. The former method has the advantage that you cannot experience an ODBC failure 90% of the way through a big transfer.
However, I think the key to the problem is that I could find no way to show SQL Server or ODBC the location of the applicatble workgroup information file. Perhaps SQL Server or ODBC always presents Admin credentials for the default SYSTEM.MDW file.