Logged-in users

[Miles]

Hi,

I have a site where users can log in.  This sets a cookie with their 
encrypted login details, so they can be authenticated.  There are a 
small number of pages which are user-specific ("change your details" 
forms, etc), and these are set not to cache.

When a user is logged in, a message is shown at the top of the page "You 
are now logged in".  However, nothing on the page depends on the 
individual user.

My question is, how can I organise the cache to have the most cache 
hits, given that there are effectively two versions of each page - one 
for logged in users, and one for anonymous users.  I want to 
specifically avoid each user having their own version of the page stored 
in the cache.

Thanks in advance for any wisdom anyone can share!

Miles