So far we only support defining your Gadget via script and css.  We do not yet support "xhtml"-based templates (although we are exploring approaches for adding this in the future). Therefore, instead of just specifying the HTML you want included, you will need to specify your included HTML via a simple script.

You can find a sample gadget to get you started at:
// manifest (feel free to try adding this to your page)

// associated script

// associated style sheet

I hope this is sufficient to get you started.

-Scott Isaacs

My blog that also has additional related information
(select the category from the right column)