Help me New Question here~

[sspssp]

If I use Avast the network shield, standard shield, web shield and p2p shield, do I need to install a firewall?

I'm currently using the Avast shields and I want to know if I should use a firewall like ZoneAlarm or Comodo. But I heard the firewalls make your computer slow.

And also, is it good to use AVG and turn on the AVG detecting with the AVAST shields in the same time???

Please help me~

[.: Mac :.]

Yes you Need A firewall even with avast installed.
Never Run 2 Antivirus programs at the same time, they often conflict with each other

[Lisandro]

I'm currently using the Avast shields and I want to know if I should use a firewall like ZoneAlarm or Comodo. But I heard the firewalls make your computer slow.

Network Shield is just a protection against known Internet worms/attacks. It analyses all network traffic and scans it for malicious contents. It can be also taken as a lightweight firewall (or more precisely, an IDS (Intrusion Detection System). It's not a full firewall. You won't regret using Comodo 

And also, is it good to use AVG and turn on the AVG detecting with the AVAST shields in the same time???

Take care 
Both avast and AVG could conflict... even disabling one of them you could have troubles, specially with mail scanning. Choose one of the two antivirus.