The only components you require are the 64bit CPU and mainboard for a 64bit upgrade.
You only need to choose a 64bit chipset (socket 939) that has an AGP slot.
An "nForce3 Ultra" chipset will do the job nicely I believe.
Here is an example:
http://tw.giga-byte.com/MotherBoard/Pro ... ra-939.htmThere are via chipsets as well.
I not sure if there is an nforce4 board with AGP, I haven't seen one yet.
Many will whine about AGP, but it will be some time before PCIe graphics become the standard, and when they do, you will have better video card and mainboard upgrade options to choose from, no doubt at better prices as well. Right now there is a little bit of a premium on the new technology.
There is nothing wrong with AGP graphics in the current software environment.

Mainboard: Asus P5K-Premium, CPU=Intel E6850 @ x8x450fsb 3.6ghz, RAM: 4gb PC8500 Team Dark, Video: NV8800GT, HDD: 2x1Tb Samsung F3 RAID-0 + 1Tb F3, PSU: Antec 550 Basiq, OS: Win7x64, Display: 24&