I searched all over the place for about an hour before finally running across the EASIEST solution to setting a local user account "Password Never Expires" checkbox for Windows XP. If you've tried NET USER (user) /EXPIRES:NEVER You will find that this does not work... the reason is because that is applied to the account never expiring, not the password...
So, for the easy fix to setting "Password Never Expires" on a local account in XP, open the trusty ol' command prompt and enter:
WMIC USERACCOUNT WHERE "Name='username_here'" SET PasswordExpires=FALSE
For example, on the administrator account, you would type:
WMIC USERACCOUNT WHERE "Name='Administrator'" SET PasswordExpires=FALSE
Note: I need to make the quick disclaimer that this tool is mainly only for business class Windows computers (Pro) because it is considered an "admin" tool. (I don't know about Vista home or Win 7 home) So, if you are running XP Home or the like, you probably don't have the tool :(