I'm going to be getting an Alienware mx17 laptop soon I think it's a 2011-2012 version it has x2 4870s in it I'm looking to upgrade would that be possible? And I'm guessing the CPU would not be upgradable right?
yes you can upgrade the GPUs and CPU in that machine. The CPU can only be upgraded with one from the same family of CPU's. I'm guessing yours has an Intel 700 or 800 series CPU.
The GPU can be upgraded with any NVidia or AMD card(s). You will need to use modified drivers though to run any more recent cards. The drivers direct from NVidia will not work.