I've personally found Firehol http://firehol.sourceforge.net
to be the easy, powerful iptables frontend. The nice thing about it is you can make a change to your firewall, test it and have it revert automatically if it doesn't do exactly what you want.
download the rpm, install with:
rpm -i firehol-1.273-rh7up.noarch.rpm
update the ipv4 address space:
you can then edit the /etc/firehol.conf file to do what you want. If you only route the traffic you'd like to let through, web, e-mail, etc., that would handle a lot of your P2P problems.
enable firehol on startup:
chkconfig firehol on
Anyway, it's something you could look at.