Windows Vista Service Pack 2 (SP2) includes all of the updates that have been released since SP1.
How to get SP2
The recommended (and easiest) way to get SP2 is to turn on automatic updating in Windows Update in Control Panel, and wait for Windows Vista to notify you that SP2 is ready to install. You just need a few clicks to begin the installation and the rest of the process is automatic.
To learn if SP2 is already installed
If Service Pack 2 is listed in the Windows edition section, SP2 is already installed on your computer and you don't need to follow the instructions below.