The cable from the modem itself will be a "crossover" this isn't actually a straight reversal of the connections, (as I found out way back when I started making up my own cables).
This one should do the job:
http://www.dabs.com/uk/channels/hard...quicklinx=18LY
*edit Looking at Monkeybreath's comment below, I have the Terajet CM myself so the CM200 may have a standard patch cable.. can you confirm MB?