the fact that it's a lan server probably means that you want only to make a joke to a friend... anyway I'm not interested in what you (in general) have in mind to do, this is only a support forum.
hlboom is an old vulnerability so CS 1.6 should be safe as far as I know.
For additional informations about the hlfreeze/csdos/btbp vulnerabilities read here:
http://aluigi.org/adv/csdos.txt