There are several obsitcles standing in your way of web billionairedom. These include trying to get venture capitol from rich accountants that want 99.9% of the company for a fiver investment. They also include trying to encourage friends, family, accuatances and that bloke you met once in 1982 to invest some time (or their own cash) in your project. You need volunteers to test out the site on, to help promote it, (*nothing quite like a granny in a bunny outfit outside Sainsburys to drive traffic to you site. Even if it's only Help The Aged trying to get you arrested.) But the biggest obsticle of all is you.
You may try to develop the site on your own, learning HTML, ASP, PHP, MySQL, Oricle, Java, JavaScript, Cascading Style Sheets, Wap, WML, XML, D-HTML, FLASH, Mpeg encoding, you'll start reading books on design, web site design, traditional design. You read up on articles by guru / cumegon Jackon Neilson's web site www.useit.com. You'll investigate the competition, you'll spend hours and hours diescting why Amazon works and Boo failed. Why you like ShopSmart but hate letsbuy it (or visa versa.) You look at web review pages, sign up to all kinds of mailing lists, you may even start with the First Tuesday or other VC inhibitors (OPPOSITE!!).
You may try to get others to develop the ste for you, you might pay a poor lonelty programmer like me far too little money to develop your web vision, all the while squeezing another hours free work out of the poor soul, as you demand further "tweaks" to the system that require a complete redesign of the database.
You may on the other hand dismiss your idea, or just never get around to doing anything about it.
These are not the path to true enlightenment.