The inquirer wrote an article about how NVIDIA will create its processor. The technology isn't really the problem they say, but the patents are:
Back to reality. What do you do if you want to make an x86 chip? You get a licence from the people who have one, in this case most likely AMD, Intel and a few other people. You could also buy a company that has a licence, but those licences may not be transferable if a company changes control.
There are currently four companies that can make an x86 CPU from what we are told, AMD, IBM, Intel and NatSemi. Those guys are in the clear, and the others like Via and Transmeta are in a greyer area, at least according to my sources. If you want to go X86, at the very least you need to have the blessing of AMD and Intel.
The four above companies have cross licensed each other to the point of silliness and beyond, so they are all OK with whatever they want to do. Related to this, there are four companies with a license to the Intel bus, Nvidia, ATI, SIS and one other, possibly Via, but I wasn't able to pin it down. These may allow you to make chipsets, but it most emphatically does not allow you to make CPUs...