Short answer: No, and you are already using your RAM for video operations.
Also short answer: No, you can't play GTA4 with a GF7000M.
The VRAM (or GDDR) is a fixed amount of memory on you video card. You can only upgrade this by changing to a video card with more GDDR memory.
Now, the video card manufacturers have developed a way to share a part of your RAM with your video card. This is always slower than GDDR (long physical path from video card to RAM), but is still faster than getting it from your HDD all the time.
From what I can tell your are already using your RAM, as your DXDIAG says it has 793mb available, which is more than the 64mb dedicated on your video card.
But your video card memory is generally used to store higher resolution textures, so if you can't play a game a low resolutions, then don't bother increasing the ram. It's generally only for higher resolutions.
If you really want more video memory, you could check if you can upgrade your graphics card (MXM slot). If not, then don't bother.