A little late in replying to this, but maybe this will help. To use an image to submit a form, this is the format I have used:
<INPUT TYPE="image" border="0" alt="Click to Enter!" src="images/entercdbutton.gif">
Now you will have to alter this to work with the hover button created in FrontPage. I have not tried it, as I code all of my hovers using either stylesheets or JavaScript, but the general idea is there. The important part is the INPUT TYPE="image".
Hope this helps.