Essentially to get the 4.4. OTA installed on your nexus 7, you need
1) android SDK installed with google drivers and USB debugging turned on (to get usb debugging you have to press the model number like 7 times I believe in under tablet to bring up developer mode and from there you can select it)
2) the Kitkat OTA downloaded
3) google ADB sideload drivers installed. Without these, whenever you switch into recovery mode you will always get the adb device not found error when you try to run commands from windows
So here's what you need to do for us non technical people (total time of work about 6 mins)
To install android SDK, just download the large zip file from android SDK, extract the file, and run the file labeled SDK manager. It should auto install the SDK and the google USB driver.
Then download the kitkat ota and rename it kitkat (it should auto designate itself as kitkat.zip). Place it in the platform tools folder of your extracted SDK install collection wherever that is.
Connect your tablet in USB debugging mode to your PC (to unlock usb debugging mode, tap on the build number >7 times in about tablet and you should get the option for developer mode. The USB debugging option is there). Then, navigate in windows to your platform tools folder, and press shift+left click and select open a command prompt here. then type: adb reboot bootloader
If that works that means you device was recognized in windows which it should as you have the default google usb drivers installed. The device should reboot to the bootloader and highlight recovery with the tablets volume buttons and the power to actually select the choice.
Now, in recovery you should see an android man with a red exclamation mark. Also if you have your sound on windows should give you a sound indication of a device being disconnected and reconnected around this time. Press and hold the power button and quickly tap the up volume button and it should pull up a menu where you can select apply update from ADB.
Now open windows device manager and look for an unrecognized device nexus 7; I believe it should be under portable devices. Then select update driver and select browse my computer, let me pick a list of device, and then have disk. Go to the extras folder in the extracted SDK folder collection. Then selectgoogle -> usb drivers and select android win usb. Then of the three options you have pick the one that says android bootloader interface. Finish the driver install and you should now be able to put in the much wanted command.
adb sidload kitkat.zip
Note, this method is simple and doesn't require any driver editing which was part of all the false information floating about.
The website below goes through the steps for galaxy phone, but its similar overall.