mysql_query, "like" and special characters

When you have to do a "search box" in a php/mysql website, you usually end with a SQL command like

select fields from table where field like '%what_to_search%'

but sometimes, this easy command does not run right. And "sometimes" means "when the searched string has special characters". I always use UTF-8 for everything, UTF-spanish-ci for collations, etc... Beside this, sometimes if i try to search "españa" (with the special character 'ñ'), there's no results. Then, i go to my mysql-admin program, run the query, and i get the desired result. So, why the php "mysql_query" command fails? I don't know, i tried all the tips and tricks i found on Google and nothing new. So the facts are: In some mysql servers i can't search a word with special characters (in some other servers, with the same code, i do the search and i obtain the desired result). Something happens with the mysql or php server config? I don't know, but if you search the same word without the special characters, you obtain what you searched for. If i search "españa", nothing. If i search "espana", i obtain the results for "españa" and "espana". So blow away all the special characters:

function convertspecialchars($input) { 
  $specialChars = "ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝßàáâãäåæçèé êëìíîïðñòóôõöøùúûüýÿñ"; 
  $nonSpecialChars = "AAAAAAACEEEEIIIIDNOOOOOOUUUUYsaaaaaaacee eeiiiionoooooouuuuyyn"; 
  return strtr($input, $specialChars, $nonSpecialChars); 
}