FormPreview with djangoforms.ModelForm

Question

I'm confused about which to use djangoforms.ModelForm or django.forms.Form took djangoforms.ModelForm trying form post, preview and edit with same template. post and edit work. Can you point me to an example with combined FormPreview, GAE SDK and djangoforms.ModelForm usage? I try to avoid patch the latest django and think the SDK comes with django 1.0 or newer. My form class is

class AForm(djangoforms.ModelForm):
  text = forms.CharField(widget=forms.Textarea(attrs={'rows':'11','cols':'70','class':'foo'}),label=_("content").capitalize())
  class Meta:
        model = A
        fields = ['category','currency','price','title','phonenumber','postaladress','name','text','email'] #change the order