As ever the answer is "it depends" - see this article that may provide more info:
I have a wifi network provided by a Netgear router. Can I extend it in WDS with an Airport Express?
This is one of those things where you really won't know until you try. If you need to extend your Netgear router, you really should use a Netgear device to do it to insure compatibility.
The reason for this is that WDS was never adopted as an official standard, so the chances of one device working with another manufacturers device are open to question.
If you want to try the AirPort Express, it would be a good idea to understand the store's return policy in advance before you buy.
I would be extremely surprised if it worked with an Apple device, but I suppose anything is possible.
Please post on your results if you try the Apple product.