I think if you are selling perl, then use the fastest access method available. But any decent or lack of performance from Access isn't likely very valuable information if the goal is a multi-user relational database.

Since Access is in house and thought to be usable, I bet you could get support for at least using SQL Server. I have used Perl in combination with SQL Server for a Customer Service website (Concur) and it's a very decent combination. You could use Win32::ODBC to make the database connection and it's very fast and a great way to show off the value of Perl on a Windows system.

Since SQL Server is so easy to get setup (and I suspect you'd get support internally to make it happen), I would advise avoiding Access and going direct to SQL Server (or Oracle if possible). Another option to Access would be Sybase SQL Anywhere (formerly Watcom SQL) which is a real RDBMS for smaller MySQL type applications.

of course using Perl instead of ASP, even Access can be "fun"...relatively speaking ;-)