A new type of publishing your contact form is available on 123ContactForm. You can now post web forms on your Google Sites pages in a few easy steps.
Once you’re done customizing your form, go to the Get code & Publish section and choose Google Sites in the left panel. Copy the URL generated for your form – you will need it in a minute.
Access the Google Sites page that will contain your form and edit it. Choose More gadgets in the Insert menu tab and click on Add gadgets by URL. Paste the URL that you’ve copied and press Add. When you customize display settings, it is very important to set a large height size for the gadget – at least 800 pixels. Press OK, then Save in the main view.
Get more details on how to post web forms on Google Sites pages.