as per our lifecycle policy, the Service Pack 1 for MOSS and WSS will retire in April 2010!
So if you're currently still on SP1, please consider to update as soon as possible to at least SP2!
Information about the lifecycle you can find here: http://support.microsoft.com/lifecycle/?p1=12200
Before you install SP2, read important information about SP2 in the SharePoint Team Blog!
Where to get Service Pack 2 ? Check out here -> http://support.microsoft.com/kb/968170
For all later published cumulative updates, please check here: SharePoint Update cube sheet
Further information and helpful links will be found here: Updates Resource Center for SharePoint Products and Technologies
regards, Steve Chen