Right click on your Windows desktop (on XP you have to select Properties)
Look at the Settings and resolution.
The resolution will be set at something like 1024x768.
Play around with it (move the slider up and down) till it looks right.
Better still, look in the documentation that came with your laptop or monitor and find the correct resolution and set it as that.
btw are you running a TFT (flat) screen or a CRT (old TV type) monitor?
On an old CRT you can adjust the "edges" to go in and out. You do this with the buttons on the front of the monitor.