Re: network firewall ?
No. Plain old Symantec Antivirus does not use alot of resources. However, the client that you have probably is managed by a server running Antivirus server which is pushing out virus definitions and rolling out patches, etc...However you can get the client itself and leave it unmanaged and it will not use alot of resources. In my opinion, it is 1000000000x better than Internet Security.
My Rig - Asus A8N-E nForce Ultra Socket 939 ATX, Athlon 64 X2 4200+, Seagate 250GB SATA, GeForce 6800, Soundblaster Audigy 2 Platinum eX, 2048MB PC3200 DDR 400MHz Memory...