Second, do yourself and your potential investors a huge favor. Build whatever prototype you think you need for the investor presentation. Then go and give the same demo to 20 potential users first. Then refine your demo and present it to investors. The insight you'll receive from the customer demo is invaluable! Here's another good video on this: http://vimeo.com/16200157
Third (and most controversial), don't waste your time with investors until you have a built product and paying customers. Seriously. Finding investors takes A LOT of time. And you'll have to give away your company to get investment at this stage. The general rule is to wait as long as possible before taking investment because (theoretically) your company will improve its position with time and the cost of the investment capital will go down. Find some friends and family money (< $50k). Build a product. Sell the product to 10 people. Then entertain the investor route. If you can build a product and sell a product with <$50 investment, you will be in an exponentially better place than you are right now.
Good luck and keep us posted.