Well, according to the manual 4 cirtical hits with a rocket launcher grants you a remote-controlable rocket. W00t!!! :lightning :lightning :lightning
However, I can't find the 'cirtical hit spot' on any of the vehicles. I thought the AT-AT was the most easy to hit so I played Hoth 99 times, I hit it everywhere, I even landed my snowspeeder on it and exited the speeder to shoot the At-AT from above, but I still haven't score ONE critical hit :(
For the AT-ATs, their weak spot is the neck part. What I do is lock onto the AT-AT with my rocket launcher (the defualt key is "Q") and when the circle redicule turns red, fire. For me, it works most of the time. I score a critical hit.
For remote control rockets, play Poliss Massa in the clone wars period. Be the CIS, go outside to the tank battle. the critical hit location is the back panel. just sneak behind it, fire the rockets and you get the award.