I am not aware of a step by step(though I am sure a solid google would produce something). But here is a quick go at it.
1) Create a UserProfile model to hold the extra information and put it in your models.py. It could look something like this:
class UserProfile(models.Model):
#required by the auth model
user = models.ForeignKey(User, unique=True)
middle_name = models.CharField(max_length=30, null=True, blank=True)
2) Tell your settings.py about the new class by adding this line (with the appropriate name):
AUTH_PROFILE_MODULE = "myapp.UserProfile"
3) Add a signal listener to create a blank UserProfile record when a new user is added. You can find a great snippet with directions here.
4) When processing the new user record you can populate the UserProfile record as well. Here is how I do the insert (notice the get_profile):
if (form.is_valid()):
cd = form.cleaned_data
user = User.objects.create_user(cd["UserName"], cd["Email"], cd["Password"])
user.first_name = cd["FirstName"]
user.last_name = cd["LastName"]
user.save()
#Save userinfo record
uinfo = user.get_profile()
uinfo.middle_name = cd["MiddleName"]
uinfo.save()
That is all there is to it. This is not comprehensive, but should point you in the right direction.