Plz Help me on this ....Ge Force 6600 and Intel D101 G

Recently I bought a pc ...The main board is Intel D101..It has got a on board vga 256 mb...after sharing 64 mb from the RAM..So now my RAM IS 448 mb..onboard vga chipset is a ATI Radeon ...So most of the games now require minimum 256 MB VGA and 512 RAM ..So according to the situation I cant play games with those minimum requirements..

So there are 2 options to me to solve this problem

1) Adding a new 512 MB RAM
2) Adding nVIDIA 512 MB PCI Express VGA Card

So what would be the better solution..
..
What is the difference between onboard and fixed VGA cards...?
And what is this memory sharing technology from the RAM..?

Please help me on this matter..
I am confused here..


Thanks
Animex