We could be here all day trying to explain the GPU so I will give you the short verison.
The streaming processors are what it sound like the more the marrier. Vram is a good thing and it all depends on this.
If you want to run resolution at 1920 x 1200 and/or you are using more than one monitor then it would do you to have 2GB or more of Vram. All this ties into gether with the processors.
Sorry for the short version but here is a link to all about the video card. I hope you find your info but the bigger the numbers usally means it is better and Good luck to you.http://en.wikipedia.org/wiki/Video_card