Vista video card problem!!!?

I have an ATI Radeon 2400 HD graphics card, 256mb, my computer shows that i have 1406mb total available memory, 128mb dedicated video memory, 0mb sytem video memory, and 1278mb shared video memory. But when i go to play my GTA4 game it says i only have 110 mb and the game is using 200mb. PLEASE SOMEONE HELP IT IS DRIVING ME CRAZY!!!|||Can you post your Motherboard make and model?