Well, I was thinking of using phpmyadmin as it indeed works with the DB directly, but my colleagues unfortunately won’t have much knowledge of using that. So in that way, an easy gui like ms access has would be better. Also I think it would be more convenient to just open the database in Access in case they want to sign up using a paper sheet or just by visiting our desk instead of having to login to the server and start up phphmyadmin and add them that way. This ODBC thing looks interesting though, so I might have a look at that.
Thanks for the responses so far – if anyone else has any ideas how to do this in the best way, please let me know :)