How do you catch Giratina on Pokemon Diamond?

The Easy way is to Have R4 or Action Replay( I actually don't have AR so I use R4 Cheats).You Even Must Have a Pokemon Diamond or Pearl seprately.If you have your game in the R4 then you will directly get it. First,press Y for the cheats.You will browse through many cheats and find a folder for the Pokeballs.At first you will see Masterballs.Select Them.Then Play the game and Press L+R.Now you will have 999Masterballs ! After this go to Turnback Cave (First complete the Sinnoh Dex). Turnback cave is located under Veilstone City.The 4th lake is also there.It will take a lot of time to find Giratina Inside as it is very Foggy,When you find it (If in the R4 game),You directly masterball or in the R4 Game , make your Pokemon hold the masterballs and trade them with the different one.After you get it,Take the balls and this time in R4 , make the your (not R4) Pokemon hold them and DONE ! You will have 2,4,6,8,10 or 12 masterballs and you can now catch any strong Pokemon!