download the cheat from http://cheats.gbatemp.net/ and put inside your ds in the system folder in your DS I used to use the cheat though
Do you use r4? If yes,use either CHEAT.dat or USRCHEAT.dat and not both, using both will cause some codes and games not to show up
You could also use an AceKard. Download PKMN Platinum codes via the AR Manager and save the codes as an XML. Use that XML as the code list. However, changing that also means no codes for the other games, so make a Master List (or just download all the codes and back up the XML file, rename it to your liking (i.e. AllGames.xml). That's what I've done. ALSO... use PokeSAV. It's really useful for the EVENT Pokemon. It's a dotORG site...