We used an internal app based on MS Access as a frontend to a MySQL database. We ran into lots of problems, and eventually rewrote the whole app in CodeGear Delphi 2007 for Win32. This has been a great success, although the migration did cost quite a lot of effort (training/hiring a couple of Delphi programmers, buying some third-party tools). I can wholeheartedly recommend Delphi, though. And AFAIK, integration with a MS Access back-end is certainly possible --- I once wrote a Delphi app that does just that, and it only cost me a couple of days to get a feature-complete version!
I realize this is a full programming solution, so you'd definitely loose some of the ease-of-use of MS Access for building front-ends. Then again, you can put together a database application in Delphi in 10 minutes without writing too much code --- no kidding! And since the 2009 release, the language is slowly becoming more mainstream again...
