Showing adsense on pages with content only

[993ti]

I've got my adsense code in the header but it also shows on pages with no content.
How do i change it so that it only shows on pages like forum index, forumdisplay, showthread and other pages with content?

I use a small code on my phpBB board that shows the ads in the header but by adding a small line to the php files, it will only show on pages where i want it to show.

Thx in advance.