1. Plug the device in that you need the drivers for - plug it in with USB Debugging on.
2. Click on the start menu if you have Windows 7 or Vista, then type devmgmt.msc and press enter. If you have Windows XP, then click Run, then type devmgmt.msc
3. There should be at least one driver listed where there is a yellow exclamation point. Right click on that Driver, then click 'Properties'. 
4. Make sure you are on the "Driver" tab, then click on 'Update Driver'.
5. Choose "Browse my computer for driver software" (may vary for different versions of Windows). 
6. Choose the folder that you downloaded the drivers to (they must be unzipped.)

If that doesn't work - try rebooting your computer. If it still doesn't work, not much I can do, you would have to use the SDK manager.