When you request a new password, the ResetPassword method is called.
That method will use the password properties you define in web.config.
Modify your web.config as follows, at minimum :
<system.web>
<membership>
<providers>
<clear/>
<add name="YourMembershipProvider"
....snip...
minRequiredNonalphanumericCharacters="0"
minRequiredPasswordLength="7"
/>
</providers>
</membership>
</system.web>
Notice : I snipped off some properties in the "<add name... >" section,
so that the settings you are asking about would be clearly read.
Substitute the name of *your* MembershipProvider, of course.
The random password created by the ResetPassword method is not guaranteed
to pass the regular expression in the PasswordStrengthRegularExpression property.
However, the random password will meet the criteria established by the
MinRequiredPasswordLength and MinRequiredNonAlphanumericCharacters properties.
More info at:
http://msdn2.microsoft.com/en-us/library/system.web.security.membershipprovider.resetpassword.aspx