You're not going to get a quick/brief answer on this one, unfortunately. =(what the f... so a ditto with good iv will always produce good ivs? and a ditto with bad ivs will always produce bad ivs?
Read up and edumacate yourself:
http://www.smogon.com/forums/showthread.php?t=20653
(Section THREE, under "How the game provides IVs to an egg")