You have a couple options available to you depending on your actual needs, and some other criteria.
First of all, what is the size of the access database? This is important because your limiting factor, naturally, is the 56K dialup from the remotesite. If the database is of any substantial size, then you won't want to set up a remote access network connection from the remote site or VPN, causing the database to be downloaded to the remote site just to open it. It's likely that this option will not be practical, although it is possible.
The second option that comes to mind, is a remote control situation, where the remote site will control one of the main office boxes through the internet connections, using a commercial solution such as Windows Terminal Server, or Symantec's PCAnywhere. There are other commercial products as well as shareware (example, Remotely Anywhere) products, etc. These products only send the screen, keyboard and mouse activity through the internet connection, and therefore, will have reasonable performance through the 56K dialup (the actual processing is done on the host in the main office). The drawback to this option, is that while a session is in progress, the host box at the main office is in useby the remote site and not available as a local workstation.
The third option that I can think of readily, is to set up access of the database through Active Server Pages (ASP), or a non-Microsoft webserver solution that can connect to the Access database for server-side processing. For the ASP option, you'd need to set up PWS (Personal Web Server) or IIS (Internet Information Server) at the main office, and create the appropriate ASP srripts so that the remote site can access the database through a browser. This option would require programming of the desired functionality on the webserver.
Hope this helps.
--cnh