You'll probably get more conversions if you send people to a pre-sell page first. If you want to direct link to the sales/offer page, then I believe you can do that in the AdW0rds C0ntent Network. If you're using the AdW0rds Search Network, then your chances of being able to direct link to the sales page will be very slim because last time I checked, G allows only one ad per destination URL. They did this awhile back to clean up the affiliate clutter in the sponsored links.