The filename was something to the effect of:
path\User on computername at time.txt

the script looked something like this:

--------------
$file = @userid + " on " + @wksta + " at " + @time + ".txt"

del $file ; this keeps it current
$fo = open(1,$file,5)
$wl = writeline(1,@logonserver)
$fc = close(1)
-------------

It created a 1k file and it could be sorted on filename or date in explorer. It wouldn't tell whether they were logged in currently, but it would tell from what last computer they were logged on from.

hope this helps?