Which shall I choose?

I wanting to upgrade my old PC which is running pentuim 4, upgrade it to intel core I3, but I Also want to buy a new xbox 360. I love to play games, but also listening to music and watching YouTube video. I already own a iPhone 3GS, so which one should I buy xbox 360 or upgrade my PC? And where could I get the latest xbox 360 kinect with 4 or 8 gb hard drive which cost at $339, but I want to pay by monthly installment instead of one shot payment. Either by credit card or cash. Thank you