some time ago i tried to do the same thing with the FrontPage generated hover button. i concluded it could not be done. i created by own hover button using onmouseover and onmouseout. i suggest you do the same. in fact i suggest you quit using all of the FP generated effects as they all have brick walls you will find as you use them.
try something like this:
<input style="background-color: #FF0033; color: white; font-weight: bold; width: 150; position: absolute; left: 15; top: 20;"
type="button" value="Button Text"
onclick="pur your href here"
you can play with the colors and other parameters to get what you want. put your link in the onclick statement. there you need to include the target= as noted above by Stefan.
sorry - not the answer you wanted, but i have been there with FP. it is a great first learning tool, but you outgrow its limitations fast.