what type of window is it being displayed in? i take it is a black cmd shell window??
i would love to hear of a way to do it but i reckon it would take some effort.
i had a similar issue/problem but wiggled out of doing any extra work.
you might want to consider
1. creating a custom exe or control which you can output your info to
2. create you logonscript as an exe with GUi in its own right, VB.net,VB6 etc, you might find it runs faster as well and then you can control what the window looks like
3. i opted to keep central logs of when users logged on which gave an indication who was killing the script. then send a few well worded emails automatically to them about the dangers of killing the script and that is a company requirement that it should be run.
ps. even if you do get rid of the X persistant users will kill it in taskmanager etc so perhaps opting for all the approaches mention wouldnt be wise...good luck