Html-ActionLink as a button or an image-not a link
Apply a CSS class to the htmlAttributes object.

<%= Html.ActionLink("Button Name", "Action Name", "ControllerName", new { @class="classname" }) %>

and then create a class in your stylesheet

a.classname
{
 background: url(../Images/image.gif) no-repeat top left;
 display: block;
 width: 150px;
 height: 150px;
 text-indent: -9999px; /* hides the link text */
}