Then, the sad news is that Apple has designed their "extend a wireless network" feature to use proprietary settings that only work with other Apple routers.
That is not to say that it is impossible for the Express to extend a 3rd party network.....(no one has tested very router to know for sure).....but let's say that it would be highly unlikely that the Express would be able to extend the Netgear network.
If you have the time, and want to try, we can provide a few tips if you can tell us what operating system that you are using on your Mac or PC.
What the Express can do is "Join" the Netgear network, so that it could be used for AirPlay or to connect a compatible remote USB printer. But....the Express does not "extend", "repeat", "boost" etc the wireless signal when it joins a network.