I have been trying to install ACR Update 6.5 on my MacBook Pro running 10.6.8 and CS5. I have tried running the updater from Photoshop and downloading the update and installing it and I get the same error every time.
Photoshop Camer Raw 6.5 Update
There was an error installing this update. Please quit and try again later.
The 3.5 upate for Lightroom installed without an issue.