Hi! I've never been to Capetown myself but have many friends who live or go in summer to train.
3 x world Champ Aaron Hadlow spends time there when he is not on the PKRA. His website is www.aaronhadlow.com/
Why not contact him and ask a few questions. I know he would be happy to give you advice.
Another person you could try is www.petragoeschl.com/
She is an ex pro windsurfer/kitesurfer and now does photography in Cape Town over the summer period.
Hope it helps..

Hi Jeremy I was in Capetown October 2004 and will be going back this Christmas. I have a brother that lives there. The main Kiting area seems to be from Milnerton in the south to Blouberg further north If your based in the city. The average winds are SE at about the 20 knot mark through summer. The southeaster is cross off South of milnerton and no one kites further south. The wind tends to be a little gusty as it has blown across the cape flats. it gets better the further north you go. You can also kite at Muizenberg the wind is onshore and there is small surf, there is also Strand a bit further east. These two spots are on False bay so surf is small but the water is a little warmer than the Atlantic side. A car is a must in Capetown as it is made up of lots of little hamlett's, and there is no public buses. There is kiting all over the Cape, Langabaan as stamp points out is great The best spot I kited was witsand on the breeder River mouth. It's abit off a strange town with the feel of the Old South Africa but awsome flat water and good surf bump and jump with in five minutes walk.

Be careful anywhere in RSA there are plenty of poor people who will kill for 50 aus dollars. Keep your wits about you and don't look for trouble and you'll be fine