Its a big update yes, raw file says its 577.4 Mb on five languages. If you want to reclaim some disk space after applying the SP2 you can run this update cleanup tool that is included on the SP2 install – compcln.exe
Windows Component Clean Tool (Compcln.exe) can be used to remove the files that are archived after Windows Vista SP2 or Windows Server 2008 SP2 is applied. It also removes the files that were archived after Windows Vista SP1 was applied, if they are found on the system. Running this tool is optional.
NOTE AGAIN: You cannot uninstall Windows Vista SP2 or Windows Server 2008 SP2 after you run this tool on an image.
So to run this tool just go to your Run command or in Windows Shortcut thats (Win + R), then type compcln.exe
This command prompt will appear and all you have to do is type Y for yes.
This will perform cleanup with in a few minutes, better grab a coffee or do this on lunch while you are away.
After the cleanup finishes, the command prompt closes and you the space has been reclaimed.
More info are available on the Windows Vista Service Pack 2 Deployment Guide at TechNet: http://technet.microsoft.com/en-us/library/dd335037(WS.10).aspx