How to know how much memory your computer has in Windows XP?

1. Click Start and click Control Panel.
2. In the Control Panel, click on Performance and Maintenance.
3. Under Pick a task..., click on See basic information about your computer.
4. On clicking "See basic information about your computer" link, System Properties dialog box opens. The General tab will be selected by default. Under Computer, Windows will show how much memory is on the computer.

You can also right-click "My Computer" icon and clicking on Properties to view the System Properties dialog box.