Run the following & post results:
iptables -L; iptables -t nat -L; iptables -t mangle -L
Post your /etc/httpd/conf/httpd.conf file.
In which dir are you storing the html files that you want your Linux server to serve?
Are the 3 computers that you specified the only ones on the network, including cable Internet modems & routers?
Please answer all the above if you would like me to help you as they all relate to each other.