newbie firewall recommendation

[Richard Cochinos <richard@theory.org>]

Hello all-

This is very much a newbie question:

This is the first server I have set up. It was running behind a firewall
on a router however I encounterd problems getting to ports 22 and 25.

Placing it on its own IP (outside of the LAN) has cleared up the port
issues however I need to install some firewall software to protect it.

What are your recommendations?

This is a very simple server - X hasn't been installed - so any GUI
interfaces wont help me. Ideally I want only to open 4 ports 22,25,80 and
443.

Cheers,
 -richard