The second video was already confirmed fake by both Bungie and IGN.

I was going to say the first video actually looks real but JaggedSac brought up a good point. None of the spartans in the teaser were wearing Mark V or VI armor so that would either mean its fake or that you can unlock that armor in the multiplayer. As of now I'm not sure but if it is real the animations and graphics look pretty impressive.

Can you or someone else please link me to the confirmation of that second video being fake?

I'll look for it but an easy way of telling would be simply to look at murder mode. Murder is an act associated with the killing of innocent civilians. Since this is war and the term doesn't apply to the covenant then having that feature would not make any sense.

Not to mention having a feature called murder mode in a game would be highly controversial and unnecessary when they could just name it Assassination mode. Finally why would the person cover the screen at the last second?

Also if you look closely at the menu screen the game starts to load a split second before he presses A.

OK I'm going to settle this debate once and for all since I'm tired of it being brought up over and over again.

First here is Sishka a Bungie employee commenting on the leaked video

http://www.bungie.net/Forums/posts.aspx?postID=40665990&postRepeater1-p=1#40666090 

Second here is a post describing the audio they used in the menu screen, clearly a song from a previous Halo game.

http://carnage.bungie.org/haloforum/halo.forum.pl?read=963261 

Thirdly go to 0:16 in the video and read the text. It says exclusivity instead of exclusively.

http://www.youtube.com/watch?v=kQi5sh0lfvs 

Finally go to about 1:30 in the bellow video and look in the background to see what the real Halo Reach beta title screen will probably look like

http://gameinformer.com/b/features/archive/2010/01/12/meeting-the-reach-team.aspx 

Finally my brain tells me that if this was real all he had to do was show even 10 seconds of gameplay instead of making a huge show about pressing the button on his controller.