I DESPERATELY NEED HELP WITH POKEON PEARL! (read below) ?

ditto only comes at certain times.if u talk to a girl in Dawn's house(in rowan's lab's town) she will tell u what pokemon is available for the day. if she tells u that ditto is available, go to the place where she tells u and catch it. what is the guy saying when he wont accept the fossil? just keep on trying to catch cresselia. it will take some time.