Garageband '11 software update downloads but won't install

I recently had to wipe my harddrive and re-install Lion (don't even eg tme started on THAT). I had already purchased Garageband '11, so I just slipped it on to a USB with all my other crap so I could just move it over. I did sucessfully, but I still had to download the 2.something gig full instillation package. I did successfully. Now when I go to my software update the 1.2 gig full instrument package update pops up. But twice I've downloaded it, and when it began to install, it's stopped and said the same thing, something like "Update can't be installed. The package (?) might have been corruped or tampered with while downloading."

I've tried downloading it by itsself and with all the other updates. With the same result. When I attemptedto download it with the rest of my software updates, it stopped ALL of them from installing. But when I tried to install the other updates individually, they were successful.

Does anyone have any idea what could be causing this problem? I don't know where to start. It's wasting me time and is so frustrating.

Oh, and if it help, I'm using a 13" white macbook from 2009 2.4 GHz Intel Core 2 Duo processor running lion 10.7.3