I had to hook up 4 Nexus 7s (2012) on Windows 7.
After much trials, tribulations and many errors, here is what I had to do, for EACH device.
Plug in the Nexus 7 using USB. Watch it fail to install one out of 4 drivers.
Now, Computer -> Manage -> Device Manager -> Right Click on device -> Uninstall
NOTE: Check "Delete the driver software...". This buys you some time
-> OK
Unplug USB, wait 5 secs, plug it back in.
Windows tries to install a driver.
BEFORE it can complete, Right click on the device that appeared in the device list
and select "Update driver software"
Gotta be fast here. Time is of the essence. If you are slow, delete and repeat.
Browse to the Google driver ( \extras\google\usb_driver ) -> OK
Try connecting via Eclipse..
For me, at this point, the stupid Nexus was asking whether to accept a key.
Say OK, and I was all set. Not fun...