validation controlled on button event

 hi all
           i m searching a way to activate validation controlls on button click event. suppose i have 5 text boxes having required field validtions and expression validation. as i enter wrong text in text box it shows error message on the sopt and does not allow me to move further .i want it shoud allow me to fill other fields as well and show the error on button event when i submit it
regards
zeeshan
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