I must echo Mike's comments about not having a large list in order to get going. The truth is - it does not matter! You can still make an impression on a potential future jv partner by promoting their product to your list first........and the best way to get noticed and make lots of affiliate sales is to offer a powerful bonus as an extra incentive for people to buy via your link.
I did just that, and ended up coming 3rd on Matt Haslem's Optin Accelerator JV contest even though my list is quite small compared to the more established marketers.
Now, of course, people notice this, and then they start coming to you!
So, Tom, dont be put off starting with a small list. Just be a little creative when it comes to offering an extra bonus. If you follow the other marketers you can pick up some really good idea for bonuses. For example, personal coaching or offer one of your own products completely free. Just make it so people actually want to have it.