If it's for a laptop, 99% of the time you can't upgrade it. And if you are asking, I'm sure you don't have one of the 1% of the laptops with an upgradable video card.
Unless you have a laptop older than 4-5 years, whatever video card and hardware you have should run Windows 7. Just make sure you have at least 1gig of RAM. It may be slow, but not any slower than XP.