A few things come to mind.
First, the lighting is the single most important element. Shoot at either early morning or late afternoon when the sun casts a nice warm glow of light on the car. DON'T shoot at anytime around noon. This creates horrible shadows and washed out colors.
I would have said set a small aperture on your camera for most depth of field, but you probably cannot do this with your camera.
Also, a tripod, remote cable release, low ISO, and mirror lock up, but again, your camera is not capable.
Here is the biggest problem I see with your scenario. Why are you shooting with a lake in the background? Think about it. A car is not a boat. A lake has no point as a background for a car shot, and if you are not careful, you can make the car look like it is trying to be in the water. I'm sure Lake St. Claire is very beautiful, but it has no relationship or meaning being a background for an auto photo. Plus, what do you want your subject to be, the car or a lake? By trying to incorporate each in the shot, you are detracting from both.
Find a place such as a strip of road, or an unused race track, or the side of an old garage, or an abandoned drive in. Just something that says CAR! If you were taking a shot of a boat on a trailer, then the lake background would be fine. See my point?
The Powershot is a decent little point and shoot, but it is not truly the proper camera for something like I think you are wanting. It is designed for snapshots and does not give you the control needed for this type of shot. Still, you can get a decent photo if the lighting and background compliment the car.
steve
