Big part of the puzzle is to build value in your potential cofounder's eyes from your past ________ experiences. It is a two way street: your cofounder should need you as much as you need him. -Zaid
I'm talking from personal experiences of my own so there is no point of disagreement;)
That said, you're right: people love "winners." The trick is you don't have to have sold a big startup to make a reputation. Even before my startup went live, I started getting emails from people across the campus about their ideas and working with them. That's when I realized a lot of attracting folks to work with you is about PR - backed by a real plan and intelligence.