VISTA got a decent enough firewall which blocks 2 way traffic. If using XP, KIS is recommended, for VISTA KAV is enough, but of course, KIS has more advanced firewall than VISTA built-in firewall.

But for simple users, i thnk they should just stick to VISTA firewall...well, at least if i'm installing for somebody else so that they don't bug me with too many questions...LOL.