App Store keeps on trying and failing to update iMovie and iPhoto on Mountain Lion
If the apps show up in "Purchases" up can Control + Click in the item in the Purchases list and select "Hide Purchase..."

That may do it for you.

(Seem's like whoever had the laptop before you was up to some software shenanigans).

FWIW There is a file (/Library/Application Support/App Store/adoption.plist) that looks like it keeps track of pre installed versions of iLife so you can get updates from the App Store.