Good advice all around...I went to a dermatologist this week for a followup visit on some lab work, and although it wasn't particularly enlightening, I think it's good to have that expert confirmation that one indeed has male pattern baldness before starting on a regimen.
My dermatologist, oddly enough, didn't seem that knowledgable about some of the products available for hair loss. He wasn't familiar with Nizoral as a member of the great trifecta of treatments, so I had to do a little educating. His lack of knowledge was a bit disconcerting at first, but he was extremely open to what I was saying and the treatments that I described. In the end, I felt almost as though I was basically telling him everything to prescribe me. This website was an amazing resource in the whole process. I had printed out the clinical trial analysis of Propecia's efficacy from .2 mg - 5 mg, and the doctor actually took it from me and read through it during the visit. He had no problem with me taking Propecia initially every other day or taking .5 mg every day.
BTW, if you feel informed enough, don't let the dermatologist dominate the visit with long-winded explanations about DHT and how it works. My Doctor tried to do that, and I had to sort of interject some of my concerns and let him know that he wasn't dealing with a complete hair loss neophyte. Especially if you're paying for a visit out of pocket (like I did), you don't need to waste your money on a Hair Loss 101 lecture. My advice is have a laundry list of substantive concerns and get his/her take on things like internals (supplements) and topicals or whatever interests you. Hopefully you'll be fortunate to either have a dermo who knows his stuff or one who is humble enough to let you dictate your own treatment plan. Good luck.