DOS network issue: no communication with serial cable

Hi! I've been trying to network a DOS computer with a Win98 one (in DOS mode) and am having problems. I'm using a serial cable to connect them and the NSLAN program. It used to work fine--when I was using a parallel cable. I can't use the parallel cable anymore because both connections are filled with a parallel Zip100 drive. The problem is that, no matter how I set the network up, there's no communication between the two computers at all. Now, I'm not in front of the two computers right now--they're at my mother's house. Can anybody help me?

 

Do both systems have a modem?
Or if that serial cable in a null cable you could maybe use a tool from here
http://www.resoo.org/docs/dos/free_software/comm1.htm
zip looks good - links
http://www.filewatcher.com/m/zip221.zip.50531-0.html

 

Thank you for responding. I think only one of the computers has a modem. I checked out the first link but don't recognize anything. I don't know exactly the type of serial cable I'm using, but I think both ends are 9-pin female.