ONBOARD GPU

Question

My motherboard has a single Nvidia 6100/Nforce 450 chipset & the onboard GPU is a Nvidia 6150SE. Im just wondering whether this particular onboard GPU has its own memory or is it still sharing with the memory RAM. In windows display properties it says that it has 256mb memory but I noticed that that my 1gb RAM is only sharing 64MB of memory. I confirmed this in BIOS setup. What does this mean? Can anyone offer an opinion about this dillema? Advance TNX!