var downStrokeField;
function autojump(fieldName,nextFieldName,fakeMaxLength)
{
var myForm=document.forms[document.forms.length - 1];
var myField=myForm.elements[fieldName];
myField.nextField=myForm.elements[nextFieldName];

if (myField.maxLength == null)
   myField.maxLength=fakeMaxLength;

myField.onkeydown=autojump_keyDown;
myField.onkeyup=autojump_keyUp;
}
function autojump_keyDown()
{
this.beforeLength=this.value.length;
downStrokeField=this;
}
function autojump_keyUp()
{
if (
   (this == downStrokeField) && 
   (this.value.length > this.beforeLength) && 
   (this.value.length >= this.maxLength)
   )
   this.nextField.focus();
downStrokeField=null;
}