Make sure both computers are set up to use the same user group/work group. Then you should be able to right-click on the "network neighborhood"/"network places" depending on win version icon and choose "search for computer"
Then just type in the other computer's operating name.
It's probably password protected, but if you're part of the same network or workgroup, you just go to start/run and type "//thenameofhiscomputerhere".
One this that may help is the computer you're trying to access go to it and go to start/run and type //and put the name of YOUR computer. It may time out the first time, but then work after that.