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()
uinfo = user.get_profile()
uinfo.middle_name = cd['MiddleName']
uinfo.save()
Adding custom fields to users in django