Seems I haven't played this game at all, I've decided to googled things for you.
To obtain Pikachu, you will have to trade from another game and you will have to have a GBA to Gamecube connecter to trade across.
To obtain Lapras, you will have to go to
Citadark Isle and Cipher Admin Eldes will have the shadow Lapras which you will be able to snag from him (or her I dunno from the picture lol).