You'll either need to add escaped backslashes ("\") so that they get included in the output, or use escaped double quotes within the JS, or you might find it cleaner to use the "heredoc" method of quoting:
// escaped backslashes:
print "<a href='login.php' onmouseout='MM_swapImgRestore()' onmouseover='MM_swapImage(\\'Image5\\',\\'\\',\\'images/siteImages/buttonLogInOver.gif\\',1)'>";
// escaped double-quotes:
print "<a href='login.php' onmouseout='MM_swapImgRestore()' onmouseover='MM_swapImage(\"Image5\",\"\",\"images/siteImages/buttonLogInOver.gif\",1)'>";
//heredoc method:
print <<<END
<a href='login.php' onmouseout='MM_swapImgRestore()' onmouseover='MM_swapImage("Image5","","images/siteImages/buttonLogInOver.gif",1)'>
END;
// note that the preceding END; line must have no leading white-space