Maximum PC

I've got a DLink DIR-655 (Revision B1 router) and I'm trying to set up a file serve running Windows 2003 Standard. Anyway, I want to configure my router so that it will always give the server a pre-determined IP address (so that I can configure the client computers to use the static IP address for the server).

Does anyone know how to set static IP address for devices on D-Link routers? The router is a retail router, not an enterprise/industrial type router. Just your normal store-bought router.

I would do this on my own '655; but, I have it running in AP-Only mode. So, I turn to the online DIR-655 emulator.

Anyhoo...
Network > Network settings. Scroll down to 'add DHCP reservation.'
Check the 'enabled' box, and enter the computer name (its network name), desired IP address (IIRC, it must fall within the router's DHCP range), and MAC address for the computer in question, and hit Save.

Since the server is set up to get an IP address automatically, and DHCP rules state that a client will first try to request the same IP that it previously had, a reboot probably won't give it the new IP.
You'll likely need to run a Repair on the server's network connection (do this logged in locally - not via RDP), or an ip reset (netsh int ip reset, from a command prompt.)

OK, but adding the DHCP Reservation will force the router to give the Server the given IP address (even after reboot of router, or after power failure, etc--providing it doesn't loose the settings)?

That's correct.
It's not often, though, that a router 'forgets' its settings - normally, that only happens if you hit the reset button.