Xbox 360 blocking, parental control

[Ed D.]

Hi,
     I have a friend who's a single mother, that has
a problem with an out of control teenaged son
playing Xbox 360 to all hours of the night.

I suggested her having me build her a firewall
that could be used to shut off Xbox traffic to
the Internet at times when she chooses to.
For example between certain hours..

Has anybody done this?

I didn't want to re-invent the wheel if I could
benefit from soembody else's experience.

Would appreciate any advice from people
who've already done this, like what needs to 
be blocked for one.
                                   Thanks,  Ed