Avast! Internet Security and third party firewall?

[agasoft]

Hello everyone,

I am preparing myself and my computer to purchase IS.
I really like some IS features, however, I wish to use third party firewall, PrivateFirewall, because acording to my experience it have better HIPS.
Can I disable or not to install firewall from Internet Security?
I think that I saw someones signature that stated using Avast IS and Outpost firewall but I am not sure about it...
And once another question, acording t your experience, does Internet Security on any way using more computer memory, e.g. did you noticed slow down or something different in comparation with Free AV?

[CraigB]

When installing avast choose the custom install then you'll have the ability to pick what features you do or dont want, avast uses very little resources so you should have no problems in running it even on the old and slow systems

[ajey]

You can also go for pro antivirus which doesn't have the antispam and firewall module.Except them everything Found in internet security is present in pro antivirus too