The expression validator is not supported on the client side; that would require a clinet-side version of OGNL and access to server-side domain objects. It wouldn't be impossible to implement, but it would take effort.
I have a patch going in to allow manually-configured custom client-side validation that you could use to accomplish this; follow the Struts-user mailing list to see when it goes in--I'm anticipating tomorrow, but it could be as late as Friday. The patch *should* work with earlier versions of
Struts 2 as well; assuming it does I'll put it in both the S2.0 and S2.1 branches.
Your second issue is likely to be caused by providing useless parameters to the "int" field-validator; you're giving it "minLength" and "maxLength"--length has no meaning to an integer validation. You need to use the "min" and "max" parameters.