[Mythotical]

Use this instead:

<div class="cms_widget">
    <div class="block">
        <div class="cms_widget_header">
        <h3>{vb:raw widget_title}</h3>
        </div>
        <div class="cms_widget_content">
        <a href="http://www.musicgaff.com/forum/register.php target="_blank">
                <img src="http://www.musicgaff.com/forum/images/clicktosignup.jpg"  width="750" height="239" border="0" style="border:1px solid black;"  alt="Click Here To Sign Up" />
        </a>
        </div>
    </div>
</div>

Just to let you know any widgets you add should have div's like above otherwise it will break the display.