Well if this version of WAMP Server is running on 192.168.0.4 and Listening to port 8080 you will have to port forward port 8080 on your router so that connections coming into your network on 8080 get sent to 192.168.0.4:8080. This should be similiar to what you did for your other wamp server on the other pc but just using port 8080 instead of port 80.
Of course if you are not using the other WAMP Server and you router is capable of this you could forward incoming port 80 on your router to 192.168.0.4:8080. This wouldl make access from the internet easier as users would not have to remember to add :8080 to your routers ip address.
Also remember that you will have to Put Online
this Wamp Server so access from ip's other than 127.0.0.1 are allowed.
Just as a final thought, have you considered setting up Named Virtual Hosts
for your 2 sites on the other WAMP Server, the one using port 80 and already working with your existing port forwarding. Virtual Hosts allow you to run multiple sites through one instance of Apache. If this idea interests you, I can send you my HowTo on that, or you can check out the WAMP Server Forum its posted on there in a few answers already.