I have read that the usual html code for the Google Buy Now button (easily generated on the Google Checkout merchant site) won't work  because the DotNetNuke page alread has a form. I have tried it and it does not work. The typical code for Google for the Buy Now button is:

<form action="https://sandbox.google.com/checkout/api/checkout/v2/checkoutform/Merchant/123456789" id="BB_BuyButtonform" method="post" name="BB_BuyButtonform">
    <input name="item_name_1" type="hidden" value="Product 101"/>
    <input name="item_description_1" type="hidden" value="Product 101 Light Up Your LIfe"/>
    <input name="item_quantity_1" type="hidden" value="1"/>
    <input name="item_price_1" type="hidden" value="195.0"/>
    <input name="item_currency_1" type="hidden" value="USD"/>
    <input name="_charset_" type="hidden" value="utf-8"/>
    <input alt="" src="https://sandbox.google.com/checkout/buttons/buy.gif?merchant_id=123456789&amp;w=117&amp;h=48&amp;style=white&amp;variant=text&amp;loc=en_US" type="image"/>
</form>

When placing this code on a DotNetNuke page, using a text/html module, is it actually being inserted into an encapsulating form and that is why, as Google points out, it does not work? Does anyone have a work-around for this?

http://www.dotnetnuke.com/Community/Forums/tabid/795/forumid/108/threadid/214936/scope/posts/Default.aspx

Check this thread out, it will work for standard buttons but not encripted buttons, other than that there are several moduls (look in the shop ) that will do what you want.