On July 11, 2006 and October 10, 2006, Microsoft will end all public assisted support for Service Pack1 (SP1) (see affected products). After this date, Microsoft will no longer provide any incident support options or security updates for this retired service pack under the policies defined by the Microsoft Support Lifecycle policy.
So please, if you’re not running SP2, upgrade. It’s absolutely insane and highly dangerous not to be running SP2. Link here.