validar campo text numero y/o letras

[David]

Si lo único que vas a validar es que no esté vacío sería algo así:

Código PHP:

  function valboleto(){                                                           
    var x;                                                                      
    var cont=0;                                                                 
    ok=document.getElementsByName("boleto");                                    
    for(x=0; x < ok.length; x++)                                                
    {                                                                           
       if(ok[x].value != ""){                                                     
          cont=cont+1;                                                          
       }                                                                        
    }                                                                           
    if(cont > 0)                                                                
    {                                                                           
       return true;                                                             
    }                                                                           
    else                                                                        
    {                                                                           
       alert("Campo vacío"); 
       return false;                                                            
    }                                                                           
}