It depends on windows system but usually:
you go to system properties
look at hardware devices
Right click on the yellow (has to be yellow if it's driver problem) icon representing your mobile device
select property
Then go on the driver tab
select update driver
choose the bottom selection find on local computer
then choose manually
From the windows opened look for driver disk the bottom right button
Choose the driver from the folder <sdk>\extras\google\usb_driver\i386 (or amd64 for and).
Remember to uncheck the show only compatible hardware.
Then choose the driver
When windows warn your about possible incompatibility go on.
For my mobile it works, but depend on your mobile if it work or not.
Hope this help, bye.