Im looking at a new Dell Studio XPS 16 laptop, but they give you no choice for the GPU, and sell it with a ATI Mobility Radeon™ HD 5730 - 1GB, a nice card to be sure, but I'd like to make this laptop a hackintosh and install OS X, which has limited to no support for the ATI 5 series cards. So, my question is, is it possible to easily buy another graphics card and swap it with this one?
It's technically possible. But it's not the type of modification you'd want to try yourself. You'd want to have a tech with the right skills, parts and tools to do it for you. And the replacements cost a lot more than you might expect.
-> Your problem is that the ATI and Nvidia graphics modules aren't interchangeable. You can replace an ATI card with an ATI card, but not an Nvidia card.
They're packaged on different modules.
Here is a Nvidia MXM module