Problem with Drupal 6 built in "normal" caching - users getting data several days old on front page
A couple of things to look at:


Adjust the Minimum cache lifetime set at on admin/settings/performance to something better suited to your users.
Make sure you have cron tasks in place to rebuild that cache on a regular interval. You can do it using Poormanscron in D6 (Built in core in D7).
Disable any server-side performace/caching mechanisms, such as APC, memcache, varnish etc...
Disable any extra Drupal caching mechanism, such as Boost.