How to melee attack in Mass Effect for Xbox 360?

From http://www.gamespot.com/xbox360/rpg/masseffect/player_review.html?id=534409:

Meleeing isn't too good because there is no melee button, and instead you just have to come in contact with an enemy, which will automatically melee them, which can be pretty frustrating

I know this is very late, but hopefully if anyone else looks at this, then they will find this most helpful. I found that, during this mission, just as Matthew Read has said, that you use the trigger. You must have your weapon out and ready to fire and then you need to be directly beside the person you wish to melee. Once you are, hit the right trigger as if to shoot, but instead, since your proximity is so close, you will whack them with your elbow or gun.

Get really close to your target and press the left trigger.