The wheels fitted to the earlier W203 C class will be closer to the hub/brake caliper than than the correct W204 wheels.
Take a look at the chart below and compare the ET (Offset in mm) between the two.
The higher the offset the further out the wheel will sit from the hub.
I have a feeling unless you use a hubcentric spacer, the wheels from a 2006 car will foul the caliper on your car.
That is only my opinion and someone may disagree, but I'd be inclined to look for wheels with the correct offset (ET).
W203 wheels will NOT fit a W204 as the 203 wheels have 12.5mm holes for 12mm bolts, the 204 wheels have 14.5mm holes for 14mm bolts - which is why I had to sell my S203 winter wheels and buy a replacement set when I swopped the S203 for the S204!!
A 2006 C class will be a 203, a 2009 car is a 204. If you're interested, I have an immaculate set of 16" 204 alloys for sale, original Elegance spec 12 spoke wheels, I listed them in the "for sale" section months ago - and am open to offers! Courier shipping to Inverness-shire would be about £32.
thanks for the reply glad i got that cleared up before i made the mistake, chrishazle thanks for the offer of the wheels was hoping to spend as little as possible as they will only be winter tyres/wheels yours look a bit to clean for the highland winters! if you want to pm me what kind of price you were thinking ? i was ideally looking for wheels with winter tyres already cheers guys