2003 Firewall suggestions

I am new to 2003 Server and have set up a small business network using it as the DC, DHCP, DNS. as well as serving some applications. I have had a lot of problems with configuring a software firewall. I have tried Zone Alarm Pro. Couldn't confiigure it. Mabe a bad CD. I now have Nortons Internet Security 2003 installed but disabled. It broke the server upon installation. I could not configure it. Lots of errors. I have updated the 2003 Server from Microsoft, but still get various errors in trying to configure Nortons. I have tried to turn on the 2003 Firewall but get prompts to disable RAS etc. Is there a software firewalll to be used with 2003? I have found no software that lists that OS. We are currently behind a couple of hardware firewalls, but would like more security. Could someone suggest a firewall? Thanks

http://www.checkpoint.com/products/firewall-1/index.html

http://www.watchguard.com/products/edgex50.asp

http://accessories.us.dell.com/sna/productdetail.aspx?sku=A0250604&c=us&l=en&cs=19&category_id=2999&page=external

http://accessories.us.dell.com/sna/productdetail.aspx?sku=A0053819&c=us&l=en&cs=19&category_id=2999&page=external