Windows XP recent updates for SP1-necessary or not?

Hi,windows has more recent updates for XP service pack 1.Many of my friends need to know if it is really necessary to install these critical updates at all if we all have great firewall,antivirus & antispyware programs on our computers.Some believe these programs are ample protection against attacks,and that installing more updates from microsoft is just more clutter on our hard drives.
So, can an attacker still get through even though we have up to date firewalls,AV & antispyware programs running on our machines?
Thanks for any information