I have a HP Pavilion DV7 laptop, has core 2 quad Q9000, 6GB Memory and ATI Mobility Radeon HD 4650. I'm curious if I need to upgrade to play Diablo 3 decently, if i need to upgrade i was lookin at either Asus G75VW or Alien ware M11, which is a better buy?
You need for minimum: "NVIDIA GeForce 7800 GT or ATI Radeon X1950 Pro or better". So in that case, you should be able to play it smoothly, albeit at low/med graphics.
Stay away from alienware - overpriced flashy lights and thats it.
If you want to upgrade and have the space, get a desktop for gaming and then use the current laptop for any school/uni/work stuff that needs to get done on the move. You'll save yourself a ton of cash and get a better gaming rig out of it.
There's no reason whatsoever to upgrade your laptop. The Q9000M and Mobility Radeon HD 4650 are just fine. Worry about upgrading when either your laptop dies or all games are DX11. As it is, you're doing fine.