[Silver Knight]

Suggestion:
Don't constantly change someone's IP.
Have them record their various IP addresses throughout
the week, then, at the end of the week, determine their range.
Also, you can seperate multiple IP ranges with a comma.

If you feel you absolutely have to change someone's IP range constantly,
you should develop some sort of secret question/password system and forbid
them from saving the password and/or answer to their computer.