regular expression validation does not working in ie 6 and ie 7

Hello,
I want to validate password which should have atleast 1 number and one charactor,Its working in all browser except IE 6 and IE 7
I have tried following validation-
"^(?=.*\d)(?=.*[a-zA-Z])(?!.*[\W_\x7B-\xFF]).{6,15}$

/^[a-z][-a-z0-9_ ]{0,49}$/i  ^(?=.*\d)(?=.*[a-zA-Z]).{4,8}$/^[a-z][-a-z0-9_ ]{0,49}$/i 
^(?=.*\d)(?=.*[a-zA-Z]).{4,8}$
[a-zA-Z'.`-´\s]{1,40}
(?=^.{6,}$)(?=.*\d)(?=.*[a-zA-Z])(?![.\n]).*$



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