HTTP Headers for caching (PHP) dynamic pages

Hi,

I use Squid 2.6 as reverse proxy for several production websites but I
experiment problems with Internet Explorer 6.
It keeps the pages in cache too much time and a reload (with CTRL+F5)
has no effect.
I currently use the PHP session_cache_limiter() function, with the
'public' argument.
Does anyone know a good combination of HTTP headers for telling Squid
to cache without causing this problem ?

Thanks.

My squid.conf :
http_port 1.2.3.4:80 defaultsite=www.example.com vhost
cache_peer 2.3.4.5 parent 8080 0 no-query

acl port80 port 80
acl purge method PURGE
acl localhost src 127.0.0.1
http_access allow purge localhost
http_access allow port80
acl all src 0.0.0.0/0.0.0.0
http_access allow all

emulate_httpd_log on
cache_access_log /var/log/squid/access.log