A Single Product Auction

Hi all, I need a very simple website auction script. Here's an example concept. 1) A single advertising spot is shown on the homepage of a website for a time period of a week or so by the webmaster. 2) A website visitor is interested in that particular advertising spot and wishes to bid on it so he/she has to either sign up or login to make the bid. 3) The highest bid is shown below the advertising spot in real time along with the ID of the highest bidder, time left till the end of auction and maybe some other info as well. 4) Bids get higher as more and more people sign up/login and bid. 5) At the end of the auction, the highest bidder pays the webmaster through Paypal and uploads his/her advertising to the server and his/her advert is shown for the week while the bidding process continues for the same spot for the next week. 6) I would want this fully automated. As you can see it is not a complicated idea, quite simple really. Good Luck.