Video card Problem, Vista?

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!!!|||GTA4 Minimum requirements:

Windows XP

with SP3 / Vista with SP1

1.8GHz Intel Core 2 Duo, 2.4GHz AMD Athlon X2 64 or equivalent

1GB RAM (1.5GB for Vista)

16GB HDD Space

>>256MB nVidia 7900, ATi X1900 or equivalent<<

DVD-ROM Drive

Internet connection required for installation and online play



You graphic card isn't powerful enough to run the game.