This should work with the latest version (trunk) of django:
comment = forms.CharField(label="", help_text="", widget=forms.Textarea())
Hope that helps!
The Django documentation on customizing labels says it could be turned off with auto_id argument to Form constructor:
auto_id
f = ContactForm(auto_id=False)
Try this in your form:
def __init__(self, *args, **kwargs): self.fields['comment'].label = ''
But for newer versions of django i prefer Iemonad's answer