1. Go to Device Manager -> Keyboards.
2. Right-click "Microsoft eHome MCIR 109 Keyboard", select "Update Driver" ("Update Driver Software" on Vista).
3. Go to "Browse my computer for software" (XP users tell it not to install automatically and say you'll specify the location, then when it asks you where you would like it to search for drivers choose the option to choose from a list) then "Let me pick from a list of device drivers on my computer".
4. Make sure "show compatible hardware" is checked, then select "HID-compliant device" and click next. Click any remaining "OK" or "Finish" buttons after Windows has installed the driver.