The power distribution across the 20-pin and 24-pin connectors is very different between ATX 1.x and ATX 2.x (though the pinouts are the same, of course, for the 20 pins they have in common). Older systems tend to draw power from 5V and 3.3V rails, whilst newer systems tend to draw power from 12V and do on-board conversion. So if you are swapping an old ATX supply with a newer, similarly-rated supply, I suppose you might bump into supply problems. Banging in an apparently over-specced ATX 2.x supply might fix it because although you're not pulling power off the 12V, 5V and 3.3V lines in the expected manner, the 5V and 3.3V lines do have sufficient capacity.
Did you need to connect the CPU power plug for CPUs of a certain age? Couldn't tell from your posting. If I were to guess at the CPU your friend has, I'd think an LGA 775 of some kind, around 3.4 GHz??
Well, a quick post so it's probably wrong :-)