Not a daft question-- the only real way to tell however -- is to give it a try.
Zone Alarm is a great firewall--their antivirus leaves much to be desired, in my opinion.
I have no experience with EAV
There are many good/great choices for free AV's-- plus you can have one installed-- and run free online scans as a backup strategy, say twice a month.
Lists of freeware antivirus - CastleCopsWiki