Well, to start off, you need a password protected admin account on both machines. On the host machine, go to Start, Control Panel, Windows Firewall and click on the Exceptions tab. Make sure Remote Desktop is checked. Then go to Start, Control Panel, System, and on the Remote tab, choose, "Allow Users to Connect remotely" or some such.
You want to then set up your machine to accept incoming calls. Follow these instructions here.
On the remote machine, you'll do pretty much the same thing; create a new connection in network properties, choose "Connect to the network at my workplace," choose accept calls, and then choose dialup connection, putting in the phone number of the host PC.