Lets build a mac together

Alright i'm finally ready to build myself a computer. Heres my big question. If I buy regular PC parts, like a tower, motherboard, processor, ram etc. Could I program it as a mac. PC parts are far less expensive and more readily available than mac parts. My thought is that computer hardware doesn't know it's mac or pc until a program tells them, know what I mean. Plus my older bro has a ton of really good parts he doesn't want. (he built a KA computer a while ago, then upgraded again) I Think I can pull this off with a little help. Plus, If it works, I'll be able to build a few small computers to run my home functions and one for my girlfriend so that if it gets messed up i wont mind.

Installing OSX on anything except an Apple computer is against Apples EULA and therefor against the rules of Mac Forums. Sorry.