I really want to try making my own shampoo as well. I want to make one with a decyl glucoside base for a more gentle surfactant. I've been doing research on it for a few months. I hate my current shampoo and any of the ones I've liked are a bit too expensive for me to use now. I like the "shea mositure" intensive therapy ones but its a bit too expensive at $10 per (small) bottle. I might just end up forking it over after this bottle of shampoo runs out.
Unfortunately, as Dee Anna was saying, there isn't much cross over in the soap/lotion world to shampoo. To be honest, syndets are so fascinating to me and I would love to get into them with enough time and money. You can find many of the surfactants you need for shampoo at chemistry connection (save on citric).
Edit: liquid soap and shampoo are not interchangeable. Liquid soap (real soap) is potassium based fatty acids. Just like regular shampoo bars, the high pH will damage hair over time or effect it in unpleasant ways. I tried using liquid soap on my hair about 1.5 years ago and it made my hair look very dead. I do think its WAY better than using a bar soap on your hair (personally) since its easier to distribute and wash out. Plus, its already diluted when it goes on your hair. I still would highly recommend surfactants over liquid soap for your hair though.