antivirus
 

What is the best antivirus and firewall I can get for a Linux System?

Usually the best firewall is the one your distribution comes with. Clamav is probably the most common Linux Anti-virus which I believe looks primarely for Windows viruses and takes action against them as Linux is not exactly a target for viruses.

Well, in most distros the kernel firewall is enabled by default, but if you want to easily tweak it there's a program called Firestarter. As for antivirus software, ClamAV works nice. One thing though, if you're just using Linux you probably don't need it. I use it from Linux to scan my Windows partition. AFAIK there's only 14 Linux viruses and 8 of them are only "proof-of-concept" meaning they don't really exist. Compare that with thousands of quite real Windows viruses out there. Most Linux users just don't worry about it much.

iptables, is the backbone of a linux firewall system. If you have spare time in your hand I'll advice you to googling with iptables. If a careful study makes you a champ in making iptables rules, you need not depend upon any third party firewalls.

no real need for an antivirus on linux you can live without it

here a howto on firewall to get your story straight

http://www.tldp.org/HOWTO/Firewall-HOWTO.html

if i run email server and my staff read email using outlook (windows), how to make the email clean before my staff download it to their computer ...

what is the best antivirus ??

If you want an antivirus- and antispam-software for mail-scanning use amavis and clamav as backend. they're not too hard to configure and work just well (in my opinion).

of course you could also use a commercial antivirus scanner...