[Freesteyelz]

Do you just want unique Header images or unique Headers for each forum? If the latter then follow below (laying out the code as darnoldy explained above):

Top of "header" template add:

<if condition="in_array($forumid, array(x))">
Header "x" code here...
<else />
<if condition="in_array($forumid, array(y))">
Header "y" code here...
<else />
<if condition="in_array($forumid, array(z))">
Header "z" code here...
<else />

Add to the very bottom of your "header" template:

</if></if></if>

Replace the "x", "y" and "z" with your ForumIDs. Notice above I've included 3 conditional fourm headers. Add more by simple copying the code. Make sure that the end </if> tags matches the amount of conditionals you use.