How to determine if SQL Server 2005 SP1 is installed

If Service Pack 1 has not installed, the SELECT @@VERSION query returns:

 Microsoft SQL Server 2005 - 9.00.1399.06 (Intel X86)
  Oct 14 2005 00:33:37
  Copyright (c) 1988-2005 Microsoft Corporation
  Standard Edition on Windows NT 5.1 (Build 2600: Dodatek Service Pack 2)

After installing Service Pack 1, it looks like this:

 Microsoft SQL Server 2005 - 9.00.2047.00 (Intel X86)
  Apr 14 2006 01:12:25
  Copyright (c) 1988-2005 Microsoft Corporation
  Standard Edition on Windows NT 5.1 (Build 2600: Dodatek Service Pack 2)