Accessing application?

I have four computers, one with winXP home and three
winXP pro, on the winXP home computer I installed a
program called Top Producer and I want to be able to
access it from the other three computers? I called the
software company and they said I needed to change my
network settings to allow the three computers to use this
application. I do not have a firewall and I am using
Norton Antivirus software and I disabled them so I am
asking what settings I need to change? Thank you.