Especially since you don't know what you are doing, on your first 
attempt, build on the shoulders of giants.  IPCOP, found at ipcop.org 
has a 25-30MB downloadable ISO that has Red Hat 7.3, snort, iptables and 
is secure by default.  Also has a nice little web page you can admin the 
thing from and grab log files of hack attempts, etc.  I use it as my 
firewall (it stand between my machines and the wild and wooly internet. 
  It has worked great for about 3-4 months now.  If you want to add 
ACID, you can, but I would add mySQL to another internal box and have 
the logs sent there for analysis.  You can read more about the reasoning 
behind this in the IPCop docs.

-- 
A Computer without Microsoft is like a chocolate cake without mustard.
-as seen on IRC