create a logoff script and schedule it.

For XP this isn't a problem because you can use schtasks:
Quote:


SCHTASKS /Create [/S system [/U username [/P password]]]
[/RU username [/RP password]] /SC schedule [/MO modifier] [/D day]
[/I idletime] /TN taskname /TR taskrun [/ST starttime] [/M months]
[/SD startdate] [/ED enddate]


/I idletime Specifies the amount of idle time to
wait before running a scheduled
ONIDLE task.
Valid range: 1 - 999 minutes.





For the other os's you have to use something else.

It isn't freeware but maybe this can help you:
http://www.ayesoftware.com/asd/products.php

I'll let you know if there is something else you can use..
_________________________
Co