Did the original owner use candybar (From Iconfactory) If he did and it's still there I believe it has a "Restore defualts" option. If not you can download at iconfactory.com (I believe it can still restore or defualts even if they didn't use it originally.)
Otherwise, if you have access to the original icons, click "get info," click the icon in the corner, copy it, and then, doing the same, paste it into the icon you want to change.