Yeah, I'm afraid this will be true
The only way you could make it support it i'm afraid is if you got a new motherboard. Is there any way you can send that RAM back and get a replacement, and cheaper most probably, speed 2700 ram?
With the 256 you already have, did you also add the 512 into this?
If so, and your computer did support 3200, this ram would be slowed down by the slower 2700 speed ram anyway since the RAM buses carrying the data have to be going at the same speed.
I would advise to get another 256Mb stick of speed 2700 ram (DDR333) to make 512mb again. You should just be able to replace it
I hope this helps