Get an E-commerce system, or buy a PHP bidding system.
http://www.oscommerce.com/
http://www.phpprobid.com/
You don't want to take on all the things needed by yourself. You'd have to worry about accepting different kinds of payments, dealing with PayPal or credit cards, etc. It's not a good path for anyone short of advanced in all web-based fields. Not to mention legal matters.. It's best to use an existing system, or better, buy one that's reputable.
Ice Cold doesn't know what he's talking about, that's hardly scratching the surface. Anyone in PHP kindergarden can do what Ice Cold just did, that's not even close to a fully-structured, multi-payment compatible bidding system. Don't get me wrong, I'm no more capable then he is of creating such a system. Nor is the OP, from what I can see.
An existing stable system is what you want, if you plan on making money with it anytime soon.