Nahrazeni retezce

Cau mam nějakej řetězec třeba "řščř+-85645gfd61vxyc/*asdf". Jde o to že potřebuju nahradit vsechny znaky krome pismen a cislic pomlckou. Nevite nekdo jak na to?

$co=preg_replace("/[^[:alnum:]]/", "-", $co);
nevim jak to veme řšč...

ikdyz... alnum by fungoval asi jen v ereg_replace
tady musi bejt bud "/[\S]/" nebo "/[^\s]/"

Dik tim preg_replace jste mi pomohli. Uz jsem to vymyslel.

$string=strtolower($string);
$vem =array("á","è","ï","ì","é","í","ò","ó","ø","š","","ú","ù","ý","ž");
$nahrad =array("a","c","d","e","e","i","n","o","r","s","t","u","u","y","z");
$string = str_replace($vem,$nahrad, $string);

$string = ereg_replace("[[:punct:]]"," ",$string);
$string = ereg_replace("[[:space:]]","-",$string);