Four steps is better for all sorts of purchases. Each bit of informations entered is a bit of effort invested in the process, making each additional step more difficult to quit (sunk costs). Making the first steps easier (and, especially, putting the payment info at the end) means the user is eased into the process. People also like seeing progress, hence the 1-2-3-4 thing (though that can also be daunting; seeing that there are many more steps to go: test this). Of course, while I think this is solid general advice, test/whatever for your own situation.

Big forms are scary. No one likes forms.