Well, I am most familiar with the openACS 3.2 and can't say exactly what may have change since then, but here is what I recommend:
nearly every page in the ACS calls [ad_header] or one of its relatives at the top, and most call ad_footer at the bottom. You can wrap header and footer information in the definition of these procs.
caveat: if you open a <table> in the header and close it in the footer (a decent way to do sidebars), any page that doesn't have [ad_footer] will be broken.
Finally, you may find a couple of pages (the general permissions come to mind) that use the old templating system. Most of these call ad_header and footer as well.
Cheers,
