You can't because no method of obtaining Keldeo has been officially released yet. Although, it might soon; because Keldeo is due to be the next pokemon officially revealed.
you can't unless you have the action replay or cheats on an R4
you don't catch Keldeo, you have to get him as an event. :(
you can get keldeo by pokecheck
You cannot catch Keldeo once the event ends but you would be able to trade with someone in order to acquire it.
you can catch it when an event is going on.
Keldeo is event-only pokemon. This means that Nintendo will distribute Keldeo for players to catch. The only other way is to cheat with Action replay, gameshark etc.
Keldeo cannot be caught in-game, it can only be received from a special character distribution.
I think it will be an event Pokemon
You can't catch keldeo in the moor belive me i tried it did't work
Keldeo is an event Pokemon and its event has not been released in regions other than Japan for now.
if you have Terakion, Coballion and Varizion then you need to have an event then go to the moor of Icarus and you will find Keldeo.
Event only. Keldeo hasn't even been released yet (June 2011)