No disrespect intended, but if you need to ask what grade of sandpaper to use to start the paint process, you really need to do some homework first. There is no way to explain it adequately on a forum such as this one.

Hot Rod, Car Craft and other magazines usuallly publish a how-to-do-it on painting. Hot Rod's Paint and Body special issue was published in the winter of 2004. Check a well-stocked magazine rack like Barnes & Noble or Borders.

Search the car magazine web sites for articles like this.

http://www.carcraft.com/howto/24820/index.html

A word of caution. If you start sanding before you figure it out, you will regret it for a long, long time.