Archive View

I know this has been posted before….
If someone views an archived post, or hits on a post in an RSS feed, they come to my page and see just that post, but with a long menu div. Because of the way my page is styled, this menu div breaks through the content, and continues down the page. Looks messy.
Is there a reliable way of either querying the referrer (probably not), or finding out if mod_rewrite is actually being used, and then having some php that does an if /else
if (view is of index.php / current post)
then (use menu div)
else (use menu#2 div)
(or have no menu div at all)
and then the user creates a menu#2 which they want displaying for single post views.
Obviously it would never be perfect due to the varying lengths of posts, but it would be nice if this could be used in some way, and it does increase the presentational side of archiving.