Very easy to do. I did them in a day allowing for paint to dry.
First off you need to get the basic car.
Only found one on ebay at the moment.
http://cgi.ebay.co.uk/SCX-Ford-Fiesta-Ra...7QQcmdZViewItemIts a 1:32 scale scalextric car.
I have a spare one somewhere.
Next thing i done was to remove the body from the base, it's only a few screws. Also prise the rear light cluster off.
Then it gets a bit more difficult. You need to mask up the windows and all the areas that you don't want to paint. The grills i found easiest by cutting a piece of masking tape and using a knife poked it into the gap (will make sence when you have the model in fornt of you.)
Once the car is masked up time to paint. I wouldn't recommed doing this in your house as the smell stays for days.
Using paint you can get in halfords give the car 2-3 coats of primer.( this is so the origional paint scheme gets covered up and gives you a good base to paint onto.) Once this has dried, about an hour minimum for each coat spray 2-3 layers of the colour you want. Again leaveing an hour or so inbetween coats. Once this has dried give the car a coat of laqure. No essential but just give the car a little bit of extra shine and makes keeping it clean easier. Once this has set (I left it overnight) carefully peel off the masking tape. Next using some superglue stick the rear lights back on. Screw the body back onto the base and you have a finished car without stripes.
To do the stripes i used some A4 sticky labes. For white strips you just cut out to the size you want. For any other colour go into paint and make a big box the colour you want the stripes and print off.
I hope that makes sence. If not i can fish out my spare one and do a photo guide.
It works out quite expensive if you don't have any paint.
Model £28 inc p&p
Primer about £7
Paint about £7
£42 is alot for a model but then again they are one offs and not many people have them

Very rough prices as i haven't bought paint for a long time.