Former World Champions - Gary Kasparov and Anatoly Karpov will play two exhibition match this year in Valencia and Paris. The first match in Valencia will start from 21st-24th September 2009 and the second match in Paris will be held on 11th-13th December 2009. Both of the tournament will consist 4 rapids and 8 blitz games.
I think the quick time control was chosen because nowadays both veteran players will find it hard to concentrate in longer time control especially after being inactive from quite some times. As you all know, Kasparov 46 has retired from competitive chess since 2005. He has occasionally play simultaneous and blitz games so he must be a little bit rusty. However recently he has train with Norwegian chess prodigy and no.4 on the world list - Magnus Carlsen for six month which would probably sharpen back his once fearsome chess ability.
Kaparov opponent- Anatoly Karpov 58, who is also seldom play this days will had a tough time considering his age disadvantage ( Karpov is 12 years younger then Kasparov * Correction- Kasparov is 12 years younger then Karpov!). Furthermore his terrible results recently didn't help much but psychologically however Karpov won the latest duels against Kasparov (2002) in New York!
All in all, i think this exhibition match will show whether Kasparov still have his old "touch" and if he does, probably we can expect a comeback from this guy...especially after his unsuccessful attempts to be the Russian President!
I read about Karpov on Chess Notes, which quote Karpov opinion about Kasparov in the book- Karpov on Karpov: Memoirs of a Chess World Champion :-
‘But Kasparov and I have nothing in common. We were formed in different eras, I in the year of social renaissance and the emancipation of the populace’s soul, and he in a time of stagnation. I came from the simple people and for a long time I remained one of them. He was singled out in childhood; elitism became an essential part of his world. For me chess was the end, for him it has merely been the means.’ (page 184)
The official site for the first match in Valencia is here (in Spanish) but i found one site that has better information and articles about the match here (in English).
The official site for the second match in Paris is not available yet but you can refer at europe-echecs.com (in France)