Avoid Firewall How Efficient Is The Premium Windows Vista's Firewall And Defender!?

How efficient is the premium windows vista's firewall and defender!? - avoid firewall

I want to install antivirus prog. Should I go up for an antivirus + antispyware software, or a full suite of Internet security for added protection and a firewall? and if so, I should always turn off the Windows Firewall and Defender, or, to avoid conflict?
I beg need a professional answer.