I need some help. I cant seem to even get to the install screen on a mac and Ive tried a few methods. Can someone point me in the direction of a good image to use?

MSI 785GM-E51 Motherboard
AMD Phenom II X2 550 (OC'd to 3.62 per core)
4GB DDR3 10600
500GB Western Digital SATA2 HDD (2 in case)
XFX HD4850 1GB
24X DVD-RW

Im just at a loss in where to start, or what image to use, and I've read on the method of installing externally from leopard but it seems very convoluted and I was wondering if there was anything more simple. Thanks for reading!