System-wide environment variables can be created as follows:

1. Right-click on the "My Computer" icon.
2. Select the "Properties" menu item.
3. Select the "Advanced" tab.
4. Click on the "Environment Variables" button.
5. Click on the bottom "New" button.
6. Enter the appropriate data.

(Those are instructions for Win2k. Intructions for other versions of Windows are similar, but may differ slightly.)

I don't know what the variable's value should be, though.