Regarding button placement, if
Save Draft (whatever you decide to call it) is going to exit the workflow, maybe you should place it further from the others - it would be disruptive if someone accidentally jerked their mouse a few pixels to the right before clicking, and got kicked out of the wizard (even though they will not lose data).
I expect sites to save the entered data (except for passwords) in later pages if I want to revisit a
Previous tab, presumably this will be the case here (else you don't care enough about users to let them save midway ;)
Next can be repurposed as
Finish for the last step. Also, for the first step if
Previous is hidden, you may prefer to keep
Next button in the same relative location instead of moving it around.
As you considered changing the title for
Save Draft in comments on the other answers, a couple of alternate suggestions:
Save and Exit : only if this is a seperate popup that will be closed automatically
Complete Later : Implicit that you will save the info as workflow is suspended