that's off topic
but i think i can help.. i got the same problem in my network at home only with 3 computers (XP pro, xp home and win98) all using zonealarm and i found out you need to add each others IP's in zonealarm itself
here's my example:
you need to add a IP ADRESS so na IP range or something.. fill in the name from the person and the IP an trust it after you did this to both computers restart and it should work