Opening page in other frame

Hi,

I have a webpage with a menu and a separate frame with a banner stating the current active menu. On selecting one of the options the desired content appears in the designated frame.
However, I also want the contents of the menu banner to change, and even another frame's which holds the submenu options.
Let's say the content page is content.php. From within that, I tried using header (Location etc. TARGET="bannerframe") but I get a warning:
Cannot modify header information - headers already sent by (output started at /www/mysite/content.php:6) in /www/mysite/menubanner.php on line 2

Is there a better way to try and change multiple frames' contents ?
I'd prefer doing it from within PHP and not use JavaScript.

Thanks in advance!
SH
.