hurleyvapor999,
Why do you want to run a server as a firewall? A firewall is better if it is a hardware firewall. And if you need to hide a network from your isp or wish to have a constant connection to the internet just buy a router. Linksys or similar work great. If you want to be more secure then run another firewall behind that. There is where your server should be if you want to serve applications. I usually run my servers on another network and not on the same network as the rest of my machines. This way I can let application from the outside get to that network and not my main network. As suggested 2003 is great, but very expensive. Linux will do most things but there is a learning curve. It sounds to me you want to experiment with a server. Windows XP Pro will do quite a few things but is is not really a server OS. But again a gateway for the internet is best handled by a simple router. Hope this helps.