Intel GMA 3100 integrated video stuck using 128MB

Hi all,
I just put together a Shuttle SG31G2 with an intel core2quad Q8200, with 4gb of DDR2 1066 ram running 32bit winXPpro. The box is for my mom so I'm using the onboard video, Intel GMA 3100. The specifications say that up to 384MB of video memory can be utilized with Dynamic Video Memory Technology 3.0.

When I choose DVMT mode in the bios and select MAX as the amount of ram it can use, only 128mb is available when I check in windows. I'm using the most up-to-date drivers from Intel.

Under system properties 3.24GB of RAM is recognized. I understand that 32bit WinXPpro will not recognize 4GB of RAM, but this is still less than 3.8GB minus 128MB (amount allocated to video). The BIOS recognizes 4096MB of RAM, so I think it's a Windows problem.

Any ideas of how to get the video settings in the BIOS and windows to be the same? And, any ideas of where that extra memory is going?

Thanks in advance for any input.