All silverlight application are embeded in html using object, for example:
<object data="data:application/x-silverlight-2," type="application/x-silverlight-2" width="100%" height="100%">
It means you still can have other html element in the page where you have silverlight. You even can create new html elements and add that to the page in your code behind.
So one solution is to create a div element in the page that is hosting silverlight and show it in front of silverlight object using z-index. And there are atleast two ways to implement this solution:
In code behind. Way to access html element in code behind file:
HtmlElement mydiv = HtmlPage.Document.GetElementByID("mydiv");
Using javascript
It is a workaround, but we have to stick with it until silverlight can embed html inside it.