Find this code in inc_header.asp (about line 90):
'## START - REMOVAL, MODIFICATION OR CIRCUMVENTING THIS CODE WILL VIOLATE THE SNITZ FORUMS 2000 LICENSE AGREEMENT
and insert your code before it.
then find this code in inc_header.asp (about line 232):
'## START - REMOVAL, MODIFICATION OR CIRCUMVENTING THIS CODE WILL VIOLATE THE SNITZ FORUMS 2000 LICENSE AGREEMENT
and again insert your code before it.
That's it.
You should put either %> and <% before/after your code or put it in response.write.