If money is no objective, then you will want a mother board with (2) 16x PCI Express slots and pick up two Nvidia Geforce 78xx and run them in SLI mode. Amd dual core is far better implemented then Intel at least at the time being. So I would go with an AMD Dual core cpu.
At the moment Nvidia has the speed crown and has better SLI (running two card together). Now the speed crown has switch times. In the future a leap frog by Ati is easily possible, remember tech is just a snapshot in time.
In the near future mother boards with more then two pci express slots will come out for the possibility of more then two? cards plus say future PhysicX (think how it's spelled) card for off loading physics processing for games that support it, and future gen sound cards...
To be honest, if you want the best bang for your buck, go with the previous best gen tech.. Reason being if you buy the best it's going to cost you an arm and a leg... and it will be outdated quickly. Or buy "previous" best gen, very affordable and still be outdated quickly.
Example, my system is a AMD Athlon64 3400+ (754 pin single channel memory), 1 gig DDR of memory, and an Nvidia Geforce FX 5700 ultra (agp). I run guild wars with 4x Anti-Aliasing, 75 mhz in 1024x768 refresh rate and the quality slider 2/3 toward the max end. The result is it looks and plays great.
When I upgrade to a new system it will be Amd Athlon64 (dual core), 1gig of DDR2 or DDR 3 (which ever is the standard, DDR 2 may have short life span with AMD since they are jumping on DDR3) or great, have at least an Nvidia 7x card (assuming 8x will be out) possible two for SLI and the mother board that has the fastest chipset (nvidia, ati, sis, via) at the time of purchase. I will sink the most money in to the power supply (if I have to replace) and the mother board for max stabilty and upgrade ability. The cpu cost will be geared towards the low or middle end of the dual cores so I can upgrade latter as an intrem step if I do. This will be next year maybe? or the following. Depends on money and what games I will be playing and how well they will run. I am looking towards Elder Scrolls 4 - Oblivion and will keep an eye for next gen FPS like quake 4, the next unreal using the currently being developed newer engine.
I personally never overclock anything there are stuff out there that don't run well with OC and you have to compensate the additional heat. OC (IMHO) great to tweak an older system to get a boost.
Almost forgot, Microsoft is exerting is control for windows vista over hardware. New features are going to be dicated by Microsoft via Direct X standards and ATI and Nvida will be competing to produce a card with the same features but for chip that runs it better... MS will have a far greater leash on video and audio. Give you another hint, Vista does not support / allow hardware accelaration of sound functions
so sound is also going to get a bit intresting. An example of the influence if ms stalls on a new update or feature for Direct X for example, Ati & Nvidia will not be introducing a new card with new features until MS has created it... So MS could break the 6 month new video card cycle...