The blinking text didnt work for all my users so I re-wrote it using an animated .gif. This version will also let you click the gif and take you to your PM box. Its a little more simple as well.
Code:
<!-- PM Blink -->
<if condition="$bbuserinfo[pmunread] != 0">
<tr><td class="page" align="center">
<a href="private.php?$session[sessionurl]"><img src="$stylevar[imagesfolder]/newpmblink.gif" border="0" /></a>
</td></tr></if>
<!-- End PM Blink -->
I put it in the navbar template right before the last </table>
I attached a .gif for you to use, but you can make your own if you like. Put the .gif file in your images directory.