you need an SD card, preferably a rather large SDHC card 16gig or something, it should also be a class 6 SD card (correct me if i'm wrong, could also be a class 4 but anyways it should be a rather fast card...)
GoPro HDs have been known to have compatibility issues with other SD cards...
you can join the GoPro cult (check my signature)
or contact the GoPro support via their website
or contact them on facebook (quickest responses here because both GoPro personnel as GoPro owners can help you out....)