If you want to pass the result as a rendered template you have to load and render a template, pass the result of rendering it to the json.This could look like that:
from django.template import loader, RequestContext
#render the template
t=loader.get_template('sample/sample.html')
context=RequestContext()
html=t.render(context)
#create the json
result={'html_result':html)
json = simplejson.dumps(result)
return HttpResponse(json)
That way you can pass a rendered template as json to your client. This can be useful if you want to completely replace ie. a containing lots of different elements.