function trim(s){ return s.replace(/^\s+|\s+$/g, '')};
IsEmail = function(f, field) {
  var string=trim(f.elements[field].value);
  return (string.search(/^\w+((-\w+)|(\.\w+))*\@[A-Za-z0-9]+((\.|-)[A-Za-z0-9]+)*\.[A-Za-z0-9]+$/) != -1);
}

CheckField = function(f, field){return (trim(f.elements[field].value)!="");}

CheckFieldSelect = function(f, field){return (f.elements[field].selectedIndex!=0);}
        
ValidateForm = function(f){
  var strError="";
  if(!CheckFieldSelect(f,"tema")) strError+="- Tema";
  if(!CheckField(f,"empresa")) strError+="\n- Empresa";
  if(!CheckField(f,"nome")) strError+="\n- Nome";
  if(!IsEmail(f,"email")) strError+="\n- E-mail inválido";
  
  if(strError){alert("Preencha os seguintes campos:\n\n"+strError);return false;}
  return true;
}