The link below will take you to the competition rules for 2008.
Look for the following sections related to the throws.
RULE 130 Throwing events
RULE 131 Shot
RULE 132 Shot specifications
RULE 133 Hammer
RULE 134 Hammer specifications
RULE 135 Discus
RULE 136 Discus specifications
RULE 137 Hammer and Discus cage specifications
RULE 138 Javelin
RULE 139 Javelin specifications