It is possible that you have another driver 'interfering' with the Android one... If you have multiple USB ports try using a different one to connect on.
There is a program that will show you all the drivers that are 'attached' to USBs, but I dont remember what its called. If I can find it before you do Ill let you know... and I think THAT is the TRUE source of your problems..
I believe you will find the 'nitty-gritty' on this little beast under the thread about the dead charger...
http://www.androidtablets.net/forum/eglide4/46757-just-knew-id-do-eventually.html
I finally got the usb driver (that you seem to already have) in my 'box'... if you need it I will PM you a link.
Oh... try DISABLING the driver that always attaches.... then disconnect and reconnect... see if that will allow the Google one to hook up....
(a possible quick&dirty fix!)
... Did you at one time have a different tablet? That would explain it... ???
Ok, finally got it! It was the android_winusb.inf file that had to be edited, at least for my Win7/64. I used the USBDeview tool you referred to above to get the proper device-id of the tablet and then put it under the Google.NTamd64 section rather than the Google.NT86x section. Then I installed the driver via the Device-Mgr and lo-and-behold I've got an Android device and 'adb devices' finds it as expected. Thank you so much for your help with this!