hmm, i was wrong to have you remove the leading slashes, the replace code is working on another section of the info window, is not effecting the link.
change the code back to:
infowindowtext: '<span style="font: 12px Verdana, Arial, Helvetica, sans-serif; color: black;"><?php echo str_replace("'", "\'", "<strong>Bob King Hyundai</strong><br /><strong>Address:</strong><br />1545 Silas Creek Parkway<br />Winston Salem, NC 27127-3757 USA"); ?><br /><a href="http://www.bobdunnhyundai.com" onclick="javascript: pageTracker._trackPageview(\'/outgoing/bobdunnmapmap\');">Visit our website</a></span>',
once you have changed it back, i'll be able to get a better idea of the true cause.