wbm2259

I came across a mobo p4i65g running Vista Home Premium. It had 512Mb of ram. I look up the specs to see what was the maximum amount of ram posible in this mobo. It said 2 GB of ram. I install two modules of 1GB each PC400. After booting up I notice that is only recognizing 1 GB. I went back to the specs and notice that in the listed OS compatible with the MOBO Vista is not listed. Is that the reason why It only sees 1GB of ram. I check device manager and there is no yellow question mark. Please advice.