You need a web server - something like apache or Microsoft IIS, which will run the PHP script when you access it through a browser interface. The web server can in turn talk to the database, and populate your website with information from it.
The browsing to html files on the network is just a bit of a quirk really - it will only work with html files, not with any scripting language. Once you have your server, you then need to be able to get to that database from the server, and program your PHP or ASP or whatever script to talk to the database.
If there are going to be lots of people using this website at the same time, then you'd be best off heading to SQL server since it's much better at handling multiple connections. Hoever, if it's internal and there will be less than 50, access should be okay. If you've got access installed on the server then the ODBC drivers should be installed with it, and you'd be best to check out www.php.net and search for ODBC or connecting to Access databases on there - there's a lot of helpful stuff.
But first port of call is to get yourself a web server.