Win XP - 3GB RAM , 2GB showing up!?

I have a 32 - bit XP SP3 and I know about the limits, about 3.2GB or something yeah? CPU-Z shows 3GB RAM, system tools show 3GB Physical memory but system information in My Comp.-View Sys. Info-2GB RAM only showing. I really want the 3GB to be used because I know it is possible. My motherboard is: GA-P31-DS3L (rev 1.0) if it helps. How can I change the 2GB to 3GB because I want the extra GB for games. I wont see any performance improvement in games will I? If XP wont show 3GB, but 2. HELPPP HOOOWW ??