Strange because if you can type Ctrl-Alt-Del then the keyboard is recognized. Did you wait a minute or two and reboot 2-3 times to give PnP enough time to prepare for USB devices? It is conceivable that your Win2k server has trouble working with the very new USB chips. Try to find Win2k USB drivers for this machine and use HIR to integrate. If it doesn't work why not use virtualization and dump it into a VM. The VM layer will not guzzle nearly enough horse power of a new server from 2008 to make your Win2k run slower than on original machine.
Jack of many trades, master of none.