Configuring the windows firewall in SBS 2003

Help, I desperately need advice on how I can configure port restrictions with ip range exclusions in the Windows firewall on SBS 2003. I have just recently set up exchange using the Connect to the Internet Wizard I was advised by our tech support rep at postini.com to enable the firewall, and refuse traffic on port 25, except for a specific IP range. I have tried to set this up in group policy and was not able to even locate the windows firewall object. maybe I have just been at this too long today, but I am really hitting a major road block, so If anyone can offer some insight as to what I may be overlooking I would greatly appreciate it