Thanks for the experience, Mulitsceeenz. I had to open up my old Alienware laptop and change out the RAM and both hard drives, and figured the graphics units were similarly interchangeable. I'm used to building desktop units.
That would explain why NewEgg doesn't sell the ATI HD 5870M by itself.
Of course you can upgrade, Multisceeenz should update himself regarding ALIENWARE gaming laptops or laptops in general, I have updated mine Alienware Nvidia GeForce Go 7950GTX SLI enabled With Gf 8800M. All removable cards are upgradable.
Maybe sometimes before during the time when laptops were just in black/white display mode existed, it was not possible.