Hi Chevy,
Thanks for the info, things may not be as dire as wadesworld makes it sound but we will see. He is right that you cannot just statically assign the DHCP address but that is not what we were gonna do anyway
The fact that your IP in system prefs and from whatismyip.com are the same tells me that your cable modem is running in bridging mode. Now that is potentially a problem because your cable provider can see all of the computers on your network and my just refuse to deal with more than say two of them. So are you able to just turn on all 4 machines and get a different IP for each of them at the same time?
If so then my bet is that there is something misconfigured on your provider's end since they are never that nice.
Ultimately, what we will do is set the firewall on each of your kids' computers so that they can only talk to who you want when. The way we do that thought depends on figuring out this networking stuff :-(
One thing that would make things simpler though would be if we could get your internal network isolated from the outside world. Is it possible to switch your cable modem from "bridging mode" into "NAT mode" where it will allow several computers to share a single external IP address? You may need to look at the manual that came with the cable modem to see if that is not possible.
At our current point in the decision tree we have:
1) Cable Modem can be put into NAT mode = 100% great we are set.
2) My ISP is ultra cool and will serve 4+ IPs to my internal network = Still OK but I don't have enough belief in human nature to think this is the case.
3) Oh no! they ignore more than 2 machines and we cannot NAT stuff. Here we are not OK, you need to buy a firewall/NAT box.
4) Oh I forgot to mention my server Mac has two ethernet cards. We could save the day in this case.
Good Luck!
-Eric