var correctos = new Array("1","2","3","4","5","6","7","8","9","0",".")
function ValidaNros(e) 
      {
 
          estado=false

          if(document.all)
          {
              codigoTecla = event.keyCode
              cadenaTecla = (String.fromCharCode(event.keyCode));
          }
          else if(document.layers)
          {
              codigoTecla = e.which
              cadenaTecla = String.fromCharCode(e.which);
          }
          else if(document.getElementById)
          {
              codigoTecla = (window.Event) ? e.which : e.keyCode;
              cadenaTecla=(String.fromCharCode(codigoTecla));
          }

          for(i=0;i<correctos.length;i++)
          {
              if(cadenaTecla==correctos[i])
                  estado=true;
          }

          if(estado==false)
          {
              if(document.all)
                  event.returnValue = false;
              else
                  return false;
          }
      }



onkeypress="return ValidaNros(event)"