server on one router, desktop on another, can they access each other?

Hi, I am setting my home network. I recently purchased a home server and now realize the computers on one router can not see the server which is on a different router.

I have a Motorala VT2442 Vonage Router connected to my cable modem. The server and one desktop are connected to this router. I also have a D-Link DI-624 wireless router in the lower level of our house. I have laptops wirelessly connected to this one as well as a desktop connected via cat5. How to I set it up so the computers on the D-Link router can see the server connected to the Motorola router?