Ok I haven't actually commented on it yet so here goes
[testing in firefox 3.5]
Background - is there supposed to be a band of white (roughly half depth of car image) at the top above the red? It look right if it is supposed to be there.
the menu - ignoring any font issues here, the actual images shift (this is down to the images being cut about 1 pixel different) left and up in some cases.
I personally don't like the font or the placement of the menu, I think for the header image a horizontal bar type menu would work better, it would also hide the 'cropping' of the image used in the header.
The menu at the bottom, never personally seen the point in them as I don't actually think I've ever clicked on them, but they seem in fashion at the moment. However yours seems out of place with your link underneath it. Maybe try a couple of different places to see if it can be balanced out more.
Prices page - it has coded text at the top.
On all pages I would add an extra line worth of padding to the text area, the box is just a little too close compared with the first page.
Now for the personal overly picky things
The car images - who took the pictures, there isn't one which isn't cropping part of the car off. The bottom image is also squashed vertically making the car look more like the 406 than the 207.
Testimonials - 2 have dates, 2 don't, personally I'd remove the dates, unless you intend to be updating every couple of months. Mari Roberts also says she'd been learning on and off since she was 17 but doesn't say for how long or gives a current age.