So I preordered Red Dead Redemption for the xbox 360, and I got the special deadly assassin's outfit that came with it,  I put in the code for it and got the downloadable content.  But how do I wear it.  I go into my outfits when I pause the game and it says you can the outfit, but doesn't say anything about putting it on.  So what do I do.  How do I fully obtain it?

I think (I am not sure) that you need to collect cloth and stuff laying around to unlock the outfits.  Not sure though I am just starting the game but I figured I would throw in my .5 cents since this post looked so lonely..

you unlock it by doing the scraps

You have to complete the scraps, I found that slightly annoying since that was a pre-order bonus and they couldnt just give you the outfit but by joining the social club you can obtain the gentleman's outfit right off the bat without having to collect scraps.