Hi Jessie,
Setting up an affiliate program to drive sales, if done right, is an extremely high touch indevor. It is not one I recommend for small business unless the product you are promoting is in an exclusive niche.
Not that you won't get people signing up to be affiliates. You will. Not that incremental sales won't occur if you just throw a software like Direct Track or join a network like CJ. You will gain some sales that way.
It is attracting professional affiliates that is difficult. They are the ones that drive real growth. The question professional affiliates will ask is why should they take time on your program when they can promote merchants with large inventories like Overstock or specific to your niche Guthy-Renker. The product you are offering will have to compete for the same space on their sites as larger merchants.
To be successful you need to:
1) Offer a great product
2) Be able to convert customers affiliates send you to sales at a high rate
3) Be flexible in terms of technology requests affiliates may have (custom landing pages for example)
4) Be competitive in your commissions
5) Have a dedicated staff focused on this channel
I highly recommend ABestWeb.com as a good resource for questions on the affiliate channel.
Feel free to field other questions if you have them.