My question would be... Why doesn't LIKE work for you? That's the best way to make a vague search...
$qry = mysql_query("SELECT * FROM table where fieldname LIKE '%".$_POST['searchterm']."%'");
You just gotta remember to put in your wildcards (%)...
If you searched for "ap", then this would give you results like:
apartment, apple, mishap, flapper, etc... In other words, no matter where in the word "ap" appears, it will find it. That's as vague as you can get.