You should download again. I had to! First one got 'buggered' somehow; likely due to very slow download & too many users trying all at once.
It's available as a separate dl now instead of Software Update.
BTW: iTunes wouldn't install due to 2 system files from 2007:
USB Missle DreamCheeky.kext
USB Missle Launcher DreamCheeky.kext
Whatever they were--they're trashed now.
I was trying to beat my buddies uptime who is running windows 7. On the upside, he got a virus today and gave up trying to get rid of it so he reformatted. I think it's safe to say that I won regardless haha