First of all, check forum ID's below which You want to add some code. For example, when link to forum is http://webflake.sx/forum/11-invision-power-board/ the forum id is 11. Next You will have to check forum id via this code in template
<if test="$forum_data['id'] == 2">YOUR CODE HERE</if>
Where 2 is Your forum id, so if Your forum id is 11, code will look like this
<if test="$forum_data['id'] == 11">YOUR CODE HERE</if>