SMS2003 Database Sizing
Sizing an SMS2003 database is an often misunderstood subject, which can cause a lot issues if not done correctly.
SMSPerfGuy has a really good article available on this subject:
http://blogs.msdn.com/smsperfguy/archive/2004/06/06/149434.aspx
And, if you are responsible for designing an SMS2003 environment for your company then you should definately take a look at the SMS2003 Capacity Planner:
http://www.microsoft.com/downloads/details.aspx?familyid=009e0c30-bded-4b95-a8f9-06037de85c57&displaylang=en