I'd recommend hiring an expert. I paid $600 to have the bathtub in my house re-glazed by a company that does only that. It was amazing. Sparkling and perfect, super easy to clean.
Before I moved into my current apartment, I demanded that the landlord get the tub refinished. They hired a jack-of-all-trades sort of handyman, and the quality can't even be compared to the amazing results I had at my house. This guy had all the right equipment (including some weird fan thing), and he did the same basic things (stripping the paint and spraying the new stuff on), but the finish sucks. I've only been using the tub for seven months, and parts of the finish are wearing off. I get a really stubborn ring around the tub every single time I take a bath. The finish isn't entirely smooth. The tub looks much better than it did before it was refinished, but it's still pretty shitty.
Seriously, go with a pro.