iTunes will not update to 10.7

When I look for new updates on my iTunes 10.6.3 it says it is the most current version when it's not. I've been to the apple website and tried downloading through there and it will go through the whole installation and at the end it says The Installation Failed: The Installer encountered an error that caused the installation to fail. The only way I can get the installation to start is to "Skip" the verifying in the beginning or else it says "invalid checksum". I'm also having the same exact problem with updating from OS X Lion 10.7.4 to OS X Lion 10.7.5. At the end it says something has interuppted the installation. Anyone have any clue what is going on with my Mac?!?