How to control LAN users?

[Bob Goodwin]

    I have a LAN with two Windows XP and one Apple Mac computers on it
    in addition to several F7 Linux boxes.  The Ethernet connection is
    via wireless Ethernet bridges at each computer and a Netgear WGR614
    wireless router at the Wildblue satellite receiver/modem. 

    I would like to be able to disable the Windows and Mac computers
    individually when not in use without going to each one and shutting
    it down.  I know, tell the users to shut them off when they leave. 
    That doesn't work, they leave the house and the computers remain on
    and connected and I am accumulating mysterious usage on this system,
    presently 82% of what I am allowed for the month.

    I can probably disable the individual Ethernet bridges via the WEP
    settings but then I may not be able to access them to turn them back
    on?  I could switch them to unused radio channels but then again
    would I be able to turn them back on from here via the LAN?  I think
    not, they wouldn't "hear" me!

    I have looked through the Netgear setup information and haven't been
    able to figure a way to control them there although it seems to me
    there should be a way and I may be missing something.

    The system works perfectly but it's out of my control, I can't tell
    whose using bandwidth as it stands.

    I would appreciate any thoughts or suggestions.

    Bob Goodwin