How to encrypt/decrypt password

I am using form based authentication. I have login table where password field length is varchar(25). I want to store encrypted in password field. I review various good articles, some of them mentioned below
http://msdn.microsoft.com/en-us/library/system.web.security.formsauthentication.hashpasswordforstoringinconfigfile.aspx
http://www.dotnetspark.com/Forum/137-how-to-encrypt--decrypt-password-and-stored.aspx
All this codes are good but their encrypted password length are more than 25 character. My problem here I cant change the length password field. Please someone suggest How can I generate 25 character encrypted length?
Avi
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