Basically I sympathize and understand what SpongeBob wants to do. But if it is for "data acquisition", I can't see where the 570J 3.8 gets you a lot more than a lesser P4. Even database management applications should run just fine on a slower machine.
But that being said, there is also no reason if you are building a new machine that you should avoid staying current with the more recent processor entry. So I won't argue the point about the processor choice, or I won't argue it too strongly, but I have some caveats for you to consider.
I considered this motherboard as a possible means to upgrade from socket 478 to socket-T LGA775, without springing for DDR2 and PCI-x graphics. That is, this is the forte' and advantage of the P5P800 mobo.
The disadvantage arises in that the board offers SATA150 onboard drive connections and controller, but no native ICH5 Intel RAID controller. If you are happy one one or two hard drives used in the conventional manner and have no need to open up the disk storage bottleneck beyond the throughput provided by individual SATA150 drives, then fine. The fact is, RAID-0 doesn't really buy a lot of extra speed except for manipulating large files, as in video-processing, for instance.
AGP graphics, at least in the generations beyond your existing choice, should be perfectly adequate for casual game applications for the near future. In addition to that, PCI-x graphics has not yet proven to show really stunning performance improvements for those types of games. And SLI at this point mostly involves taking two PCI-x graphics adapters which run individually as PCI-x (x16) and utilizing them as x8 PCI-x devices.
That being said, I looked at your price-tag here and for some reason I think you could trim it down by at least $600 if you are willing to give up the 3.8 570J processor. You could drop back to a slower and less expensive processor and over-clock it to get nearly the 3.8 Ghz speed. I'm currently using a 3.0C Northwood (~$200 retail) over-clocked to 3.6 and just shy a few hundred points from the PCMark04 benchmark Intel themselves posted for the 570J CPU. A 3.4E LGA775 processor might cost you about $315 and OC'ing it to 3.8 would hardly stress it. The reason I say this again, also, is that you have chosen to spend money on last year's memory modules that are still top-drawer, what looks like a three or four year old graphics card, and a processor that has been on the market for only a few months and costing about $780.
You could eventually move the processor to a PCI-x /DDR2 platform, but you won't be able salvage your DDR400's -- as far as I can see now with the exception of a VIA chipset and unreleased motherboard. Moving to an AMD platform, given currently available information, you have to give up the CPU and motherboard but you can salvage the memory.
I'm just saying -- if you know the value of a dollar -- you should be aware of the upgrade paths beyond your current choices.