In order to properly prepare for developing games on the xbox 360, what should my PC system specs be
Specific questions I have are:
Will I be able to compile equally on both AMD & Intel Processors
What would be an optimum amount of RAM
What are the minimum requirements for a video card (chipset / RAM).
There were some mentions of D3D and DirectX compatability (shader 2.0 support is suggested), How does this apply to XNA, and what are the hardware requirements for PC development

What are the PC development system requirements
Basiclife
There should be no difference with AMD & Intel
For RAM more always seems better, but I would suggest 1 gig but at least 512mb
For the video looks like you will need a DirectX 9 compatible card and it is suggested that it supports shader 2.0. That is suggested because that is what the 360 will do and if you want your program to use it, things will be easier if your development system supports it.
KipK
Both AMD and Intel CPUs will definately be supported. I expect that the minimum RAM requirement may be as low as 256MB, but I wouldn't use it with less than 512MB and 1GB or more would be better. If you're just creating XBox 360 games then you might be able to get away with just about any video card. If you want to run games using the XNA Framework on Windows, you'll need at card that supports shaders, ideally at least Shader Model 2.0.
Under Windows the XNA Framework is implemented using DirectX, so that how's the Direct3D requirements apply to the XNA Framework.