Card Design Software

How much will be enough, 256 MB or 512 MB How do I know if my motherboard supports a graphics card? (I have an Intel 945 with integrated graphics, is it enough; display resolution is 1440 x 900 pixels @ 32 bit Vista Basic {})

"It is imperative graphics card to run graphic design software such as Illustrator or InDesign?"
Yes

I want 1 GB of dedicated graphics card with 512 MB, but would be OK, and I prefer NVIDA graphics card.

The graphics / video card is a chipset made to the motherboard and not extensible.

The better your graphics card the better your work will look.