[Nottingham] Firewall and port issue

[gadget.pat]

Hi there,

I will be very brief as I just need some pointers as I seem to be going 
round in circles (again).

Brief outline...

My setup has a router with a built in firewall. I have two PCs running 
as servers. The windows(1) one allows access from outside of my network 
but my apache(2) server does not. I am able to access them both from 
within the network with no problems.

I'm pretty certain it is a port issue but don't know how to find out for 
sure. I have turned off the firewall in the OS running apache(2) and it 
is effectively "open". I have forwarded the ports to reflect where the 
two PCs are in my network, on the router.

My question(s), (a) What other ports would apache use in general to 
allow web access? (b) Is it a function I have not turned on in apache? 
(c) Am I just missing something really obvious?

More info

PC1 running XP (windows based server)
PC2 running OpenSuse (apache 2.x based server)
Router with brouser based setup
Port 80 used by router but no problem for windows server

Sorry, to bother the group with this but I have been trying to sort this 
for weeks now and just need some pointers.

Thanks,
gadgetpat