regex=/<b><a.*Profil\x20anzeigen(.*?)<\x2Fa><\x2Fb>/;
var ProfileText=regex.exec(PostText)[0];
regex=/<a>(.*?)<\x2Fa>/;
ProfileText=regex.exec(ProfileText)[1];

Line in PostText:
<b><a href=\"http://forum.miranda-im.de/index.php?action=profile;u=5203\" title=\"Profil anzeigen von Rolin\">Rolin</a></b>

(?<=<b>)<a>(.*)</a></b> not work in javascript, therefore I use to lines.