Forum Moderators: bakedjake
YES - with linux you definetly need a firewall.
I witnessed a root attack on my first home linux box through a dialup connection (bind for those that know). I was watching the logs and so spotted it as it happened... I still (4 years on) get port scanned everyday but always have firewall running.
Mandrake Linux comes with a firewall, shorewall [shorewall.net] - though I had problems using the graphical interface to set it up, the text configuration was flexible and fine (though if you have adsl pppoe you will have to ignore the documentation). Also Linux comes with iptables [netfilter.org] as well - kernel level packet filtering.
NO - you don't need anti virus software - though intrusion detection programs are often used on servers.
Finally - get the newest distribution that you can - and download the security patches.
HTH