Firewalls with linux (im starting to like linux)

Havent slept the past week! messing with linux distros and understanding kernel etc.

Anyways....i like linux so much...i want to change my

ISA 2006 NAT server firewall with a linux server.

Im so tiered...i cant spend another another 3 months figuring out where it is...

Any of you linux guys already know what software i should be using that supports these features"

-Word filtering
-Port blocking
-Packet filtering (streaming media)
something good if u know what i mean..

Regards,
Dave