Perhaps this one will also help. As most people already mentioned it is a matter of perseverance and developing strength. But since you are just starting out that is about the best advice I can give you.

Justin Sandercoe from Justinguitar is one hell of a teacher (best free online teacher, if not one of the best teachers ever in my opinion) and also has a video on mastering Barre chords.

Perhaps this one will help you: http://www.youtube.com/watch?v=-uJP2rWbMig&feature=player_embedded

Hope this helps.

JJ