Database maintenance is essential for the health and the performance of your SharePoint® Products and Technologies applications (EPM and/or MOSS).

Check these white papers:

Database Maintenance for Microsoft® SharePoint® Products and Technologies

http://go.microsoft.com/fwlink/?LinkId=111531&clcid=0x409

Planning and Monitoring SQL Server Storage for SharePoint: Performance Recommendations and Best Practices

http://go.microsoft.com/fwlink/?LinkID=105623&clcid=0x409

and this KB article

How to defragment Windows SharePoint Services 3.0 databases and SharePoint Server 2007 databases (http://go.microsoft.com/fwlink/?LinkId=110843&clcid=0x409)

Enjoy..