i have actually done this, and it is remarkably simple...especially on XP.
First, you have to set up your computer to answer the phone...so in network connections, create a new connection, "Set up an Advanced Connection", "Accept Incoming Connections", put a checkbox in your dialup modem, and Allow Virtual Private Connections, you can then create a user or use an existing one... then select your protocols
the easiest way to accomplish what you want to do is turn on File and Printer sharing and use that over the VPN. When you dial in, it will be like you are on a network with the computer.
Getting on the internet with this connection is a little bit more complicated. You have to set up a proxy server, analogx makes a very simple one, and it has some good instructions on setup.
if you have any questions, pop them in here...it took me a while to get this setup working, but it is absolutely wonderful.