Palin does not know what a vice president does and seems to have preferred remaining governor.
However as Sojourner's Place discusses, there has been some effort into getting her to be the VP nominee at least as far back as 2007. Check out all the links to the different sites she has on her blog.
Also questionable is how many of the links to her election sites to become governor now link directly to the McCain-Palin sites. A big question is how and why did she get on the radar so early with so little experience? Another question is why does the party seem to want to make it seem like she was just all of a sudden picked and that McCain only just now thought of her and only spoke with her once when she seems to have been being thought of for such a long time?