update : rewrote reply more clearly.
Dear monk,
why don't you use Javascript? This seems to be more suited
for these kinds of tasks than a full-fledged CGI script.
For Javascript help, look at the tutorials on
w3schools.com.
You could use a CGI script, but I advise against it. You would in that case probably use an array to hold the options and use CGI.pm to draw the page with listboxes. A button would then post a flag to the script, regenerating the page and showing the options in the other listbox. But again, Javascript would be easier for this.
If you need any help, let me know.
In the future though, you might want to give some more details about it, as to what you are trying to accomplish.
Good luck,
-- Detonite
Thank($parent($_)) if(posts($parent($_)->Useful)