firewall or antivirus???
is it like windows those are essential

Well as far as the firewall goes, any system is better off with it. You don't want those unwanted connections being made, no matter what. I like Firestarter for my firewall, but there are others. Now the anti-virus, well, it is known that the Linux To WIndows ratio of viruses is quite comedic, but just to be on the safe side all the security you can get is good. It can't hurt you, that is for sure.

Are there any other firewalls besides Firestarter?

What would the best firewall be, in terms of ease of configuration, compatibility with Apache/mail server programs?

There are other firewall, like ipchains and iptables. I am not sure which can be classed as easy to use, because its probably different from person to person.

Linux now uses iptables to do its firewalling. Ipchains was what it used in the 2.2.x kernel series and before. Just about every firewall program for linux is a front-end for iptables.

You already have iptables on your computer. You can download a program like Firestarter or you can create the firewall rules yourself. You need to be able to understand Ip addressing and ports and other terminology like that. If you would like to experiment and do it yourself start here: http://www.netfilter.org/

Or you could just do it the easier way and search google for a firewall for linux.

Another popular front-end is shorewall
http://www.shorewall.net/

Let us know if you have more questions.

i use on different machines :
- shorewall or firehol as firewall
- clamav or bitdefender as antivirus

there are more others , did you google it?

Guarddog is an easy to configure firewall frontend.

Which of the suggested firewalls can allow/deny access based on which program is asking for access?

For instance if I wanted to allow 192.168.0.101 and 192.168.0.102 both incoming and outgoing access, but to Samba only, is there a program that allows for that kind of configuration?

I know that ZoneAlarm doesn't allow that kind of configuration in Windows but Trend Micro's firewall does...

And I am currently using F-Prot antivirus for Linux.

As far as I know there aren't any programs that can allow/deny based on the program. You have to know the actual ports being used. The ports used by Samba can be easily found w/ little research.

So it can be done, but you just have to go about it in a different way.

Thanks for your help guys.