I have two computers my kids use for games and I want to use a null modem cable so they can play games like DOOM together.  I found a site on the net that explains how to set up the computers (via control panel etc.) But I get a message saying that my cable may not be connected.  I'm using a 9 pin cable--should I have bought the 25 pin instead?  Either that or I'm not doing something right in the setup.  Any suggestions?

Thanks,

Jim