RedHat Linux isn't free... however i'm confused, are you looking for an online server or setting up your own?
if you're gonna get one that is online, 1on1 are the only company i know which are offering realistic Windows Server 2003 servers + Unix Servers.
The point i'm trying to make is you have 2 systems, one which is a standard system (doesn't really matter what) and you install linux on that.
On your server you then install Windows Server 20xx - you get the security that comes with Linux (however Unix is more secure, and to be honest Windows Server is as well) ... but that way you get ALOT more at your disposal, such as php4.1x | apache 2.x | CGI-Bin | Java 2 1.4.x | SMTP/POP3 | .Net 1.1x etc...
all as standard and setup to work with each other without bugs.
Norton have designed the Firewall systems for Windows Server, which might let you know roughly how protected they are
add to this that Windows is far easier to setup, use and update that any Linux, Unix, FreeBSD, Solaris, BeOS, etc... systems
(^_^) i mean really the only true things that will open your server up to the net even on something old and basic like WindowsXP (which isn't in any form a server OS) is php or java scripting which has loopholes.
if you install something like phpBB2 as your forum, then you've just defeated the whole security you've agonised over getting into place because it opens up a whole layer of your system for its own use but also can be hacked quite easily.
The only true way to make sure this doesnt happen on your is to make sure the scripting is rescripted specifically for that system.
Tsu'va Oni Ni Jyuuko Fiori Sei Tau!
One block follows the suit ... the whole suit of blocks is the path ... what have you found?