Rentvillas, I have the mobo based on i845 too, and ATX v.2.03 PSU with ATX12v too, and what? Do you really think if the mobo uses additional ATX12V connector it will be able to support any future processors without limits? As system PSU, computer also have the mobo's own power converter for powering the CPU. What loading limit for it? Your mobo is designed when PIV 3GHz is not existing. New Intel 3GHz processor, of course, will be in FCPGA478 package but what energy it will demand at this frequency and what power voltage will be necessary for it? What you will do if the new CPU will demand, for example, 1 V voltage, and your mobo can give not below, than, for example 1.5? And what you will do if the new processor will demand extra power your mobo's converter can't support? I'm sure - install though 88 fans, the converter can burn down from an elementary overload.
I believe and I hope, what not all so is tragic, but such it is possible, therefore I think unreasonable to expect on similar upgrade.
And about memory I agree with cdogg above. RDRAM has more far the future, than SDRAM. As far as I know, some manufacturers refuse support DDR400 in the mobo's, and DDR433 it is even more difficult in this plan.