I have iMac OS X 10.5.2 Leopard. Do I need to buy FCE 4.0 or are earlier versions (eg. FCE 3.0, 3.5) compatible? I've noticed I can buy these a lot cheaper on eBay. I'm not intending to make HD movies right now but is there any other reason why I should consider FCE HD? What are the advantages of FC Pro?