First of all, AirPort Express isn't a card, it's this. You mean AirPort Extreme I assume?
Secondly, this is perhaps the most asked question on this forum.
The short answer is, in all likelihood, yes, though you may not be able to take advantage of certain third-party features like DLink's "Turbo G", for example.
As long as the router is "WiFi Certified" you're probably fine, but ask your router's vendor to be sure.