Whole house fan location
This really isn't a good idea. Whole house fans are designed to pull air from the hottest point in the house (the highest point in the living space), and replace it with cool air pulled in through the windows. Doing this through the garage would be very indirect, would likely leave stagnant hot air in some areas of the house, and would reduce the effectiveness of the fan due to all the passages the air would have to pass through.

In addition, as Ed pointed out, in some areas code won't allow venting a living space into the garage. Even leaving the door to the garage open may not be a good idea; it might let bugs into the house, and (if the fan were turned off) let garage fumes into the house.