Hmmm, I added everything like in the instructions, but I can't get the window to "popup."
I did change void(x) to void (0) to match the others as in:
<a href="javascript: void(0)" onclick="DoPrompt('spoiler');" title="Spoiler" alt="Spoiler"><img id="spoiler" onmouseover="raiseButton(this.id);" onmouseout="normalButton(this.id);" onmousedown="lowerButton(this.id);" class="markup_panel_normal_button" src="{$config.BASE_URL}/images/{$style_array.markup_panel}/spoiler.gif" /></a>
Still no dice.