And there's the chance to win the car Gareth learnt in as well as a really old one signed by JK Rowling.
The show will also feature a spoof version of Harry Potter.
CBBC's Angellica Bell officially launched the 2003 Comic Relief appeal last Friday with Graham Norton.
Since Comic Relief began in 1985, £72.4m has been given to projects helping poor and disadvantaged people in the UK.
Another £141.7m has been given to projects in Africa.
It all kicks off at 7.00pm Friday 14 March.