Web server / port forward inconsistent results

Hi, I am trying to setup a basic web server using my machines at home. I have an Imac 10.3 and a MacBook Pro 10.5. The Imac will be the Web server. I have created a dummy web page in the sites folder on the imac. My router is a 2Wire 2701HGV. I changed the port forwarding to open everything up (DMZ). I was able to see the site from my office which was good. I then tried to improve security by just opening Port 80 to the Imac and this would sometimes work/sometimes not even on my home network when typing in the external IP address. Now I have tried everything, back to DMZ, etc and can't access the site other than when I am using the internal IP 10.0.0.1 address. So, was working, now not. Nothing was changed after the point where I had the site visible using only Port 80 opened up. I simply went away from the machines. It went to sleep, I opened up and no go. Does nayone know what to do?

Some more info on this. I think it has to do with dynamic assignation of IP addresses. So what I understand is that my router reboots at some regular frequency and then gets a newly assigned IP address. I also believe that my 2 macs will be dynamically assigned when they start up as well. Is there an easy way to have the router retain a fixed address (it is a 2Wire 2701HGV) or do I have to contact the provider? Can I also fix the addresses internally of my macs?

You can setup the router to give each mac a specific ip address. Check your router docs.
As far as the outside ip, contact your provider about a static address or use something like DNSUpdate.
Most providers use dynamic ip's, they change your ip at certain intervals or whenever you restart your router.

thanks. i will look into it.