OR will I be better of updating to a PCIE MOBO and getting the new cpu, and PCIE video card?
Very much better off with PCIe and new video card. The GF5xxx series was flawed, but much more importantly, AGP is not only not seeing new cards anymore, but the existing ones are getting some insanely hefty price premiums put on them.
It's very annoying for us people who still have AGP motherboards.
So while it might cost you more to replace your graphics card now, the way things are going you'll darn close to make up that difference if you ever go to upgrade your graphics card. (And who with a GF5xxx wouldn't want to upgrade?)