A common question I see very often is can a provisional licence holder buy a car in the UK. The answer is yes, any class of driving licence can buy a car, new or second hand. In fact you don't need a licence at all.
The issue is how do you get your newly bought car home? This is where the issue of owning a provisional driving licence comes in. You will first of all need insurance if you want to drive it yourself, secondly you will need someone with a 3 year old full british licence (manual class B if the car bought is manual), finally you need to make sure the car you bought with your provisional licence is roadworthy (not just a current MOT and road tax) if you want to stay within the law.
If you don't intend to drive your newly bought car, you can have it delivered at extra cost to your home, ask a full licence holder with comprehensive insurance to drive it home for you.
So in summary you can buy a car with a provisional licence, you just can't drive it alone or without the necessary insurance and documents.
More Reading
Provisional licence and carrying passengers.
Provisional licence penalty points.
Provisional licence age is 17 and not changing in october 2010.
Recommended Product
Focus Media's Driving Test simulator for the PC, a virtual driving test simulator based on the DSA driving test.