Im surprised that nobody asked what lens is he going to be using ?
1. Put Your 40d into "AI Servo" focus mode and forget about prefocusing. This option will let You focus "on the fly" while You pan the camera from one object to another - Canon has put this option into Your camera so You can take sharp photos of moving objects without pre-focusing.
2. Use shutter speeds of at least 1/500s. Put Your 40d into "shutter priority" mode and set the shutter to 1/500s. If its a realy bright day and You have a bright lens You can use 1/1000s or even higher and You will have cristal clear sharp photos...that is if Your lens doesnt suck which I doubt. BTW, what lens will You be using ?
Canon 40d, Canon EF-S 17-55 f/2.8 IS, Canon EF 70-200 f/4 L IS.