He's obviously got a Socket 939 motherboard, but the question is, what is your brand of mobo? We need to know that more than we need to know what CPU you have. He can throw PC4400 in there, but that doesn't mean it'll just work at that speed. He'd have to bring it up that high through the BIOS which would mean overclocking his system, UNLESS he simply lowers his multiplier and raises the HTT beyond 200....so like if his system is 2.5GHz ( I know it's not just giving examples here) then instead of 200x12.5 he could do 250x10 and 250 is DDR500 which is like....PC3800 I believe?
The onboard memory controller would be his main block after a certain point of increase, so it'd take a little playing around to get it up to those speeds, but my main point is that he can infact put higher than PC3200 but he'd have to do a little tweaking to get it up to those highers speeds mainly due to the motherboard and CPU more than it is RAM limitations.