To set the dpi in Windows XP, try these steps:
Right-click the display and choose Properties from the pop-up menu.
Click the Settings tab in the Display Properties dialog box.
Click the Advanced button.
Choose either 96 dpi or 120 dpi, using the drop-down menu.
You may have to restart the PC to see the results, though if you’re done, click the OK button and obey the directions. Otherwise, choose Custom DPI from the drop-down list and continue with Step 5 to set up custom dpi settings.
Use the Custom DPI dialog box to configure the screen’s dpi.
You can choose a percentage from the drop-down menu or use the mouse to drag the ruler larger. Sadly, you cannot reset the dpi to a value less than 100 percent.
Click the OK button to confirm your settings, or click Cancel if you were just messing around.
Obey any additional directions given, such as restarting the computer. Oh, and close any other dialog boxes or windows you may have opened.
Reminder: Windows may have to install or configure new fonts and, possibly, restart when the dpi is changed.