Here's a synopsis of the "why go shampoo free":
http://community.livejournal.com/nat...ily/53928.html
The only thing I will say is that there's some debate over Sodium Lauryl and Laureth Sulfate - some people think they're evil and cause cancer, most research say they CAN be irritating, but they're not cancerous.
Castile soap shampoos are fine - you can even try Dr. Bronner's castile soap (liquid) form for a shampoo base. With the no-poo, low-poo, or homemade shampoos, the fun part is personalizing your 'recipe' with essential oils and herbal infusions - whatever your hair needs.
The no-poo standard method is based around baking soda and apple cider vinegar. The baking soda cleans the hair and opens up the cuticle to clean oils and dirt, the apple cider vinegar smooths the cuticle and gets the hair back to it's slightly acidic pH level. The apple cider vinegar rinses make your hair shine like crazy

The apple cider vinegar usually works like a conditioner and that may be enough for some people. Others use regular store bought conditioner (hopefully silicone free) or a combination of hair-friendly oils like jojoba, olive oil, coconut oil, etc (just a drop to smooth the bottom of the hair).
For more information, troubleshooting, trials, tribulations, and joys of no-pooing, check out the NO SHAMPOO MAMAS thread:
http://www.mothering.com/discussions...d.php?t=120033
It takes anywhere from 2 weeks to even 2-6 months for your hair and scalp to adjust to no-poo sometimes. In the end, most people think it's worth it and their hair looks super healthy.
Take a look at the recipe sticky for some other hints - and most importantly, the scalp massage method, which is optimal for getting rid of scalp dirt and oil and even invigorates your scalp so that it stimulates hair growth.
http://www.mothering.com/discussions...d.php?t=114069
Other great places to look are the NaturallyCurly web forums (if your hair is wavy, curly, or downright kinky).
Good luck! You've come to the right place!