I would also have taken the plastic off the Focus' seats.
They're not bad shots considering the limitations of lighting and camera.
The interior shot of the Honda is probably the best, nicely lit, all in focus, nice and sharp. You can't make the subject prettier, but you can take the best photo you're able.
Ok, with that camera you can't directly operate a separate flash, but there are two options.
1) you could buy a flash with an optical trigger (ie it will fire when the flash on your camera fires) then you can place it away from the camera to light up a different part of the subject.
2) you could buy a big portable light (like this
from Homebase) and place it to light up the darker parts of the shot like in front of the Honda.
The important thing is to make sure the colour of the additional light matches the colour of your main lighting source.
Also, assuming you have some manual control on the camera and you're using a tripod... try taking 3 shots in the same position, each with slightly different shutter speeds (leaving aperture set) so that one shot has the background slightly lighter, the next has the mid-ground lighter, then the next has the foreground exposed properly. Then combine the 3 shots in layers in Photoshop.
This is basically HDR, but with your camera, it's unlikely to do bracketted shots, so you have to do it manually. Also this isn't to give you the overly saturated HDR photos seen everywhere, but it will enable you to see details that will have otherwise been lost.
