drupal performance issues

I have a dedicated server:
Intel® Celeron® 1.8 GHz, 1GB RAM
CentOS 5, Apache 2.2.3, MySQL 5, PHP 5.1.6
drupal 6.11 with a handful modules enabled
My site has moderate number of nodes (in the thousands).

The only enabled modules which are significant are "views" and CCK.

There seems to be some issues with the broadcast function, or maybe I've lost permission to do so. I've tried 5x to broadcast everyone to remind them of the meetup, as well as contact individuals through the site, but the broadcast doesn't seem to be working, and I get an access denied on other users' contact forms. If you can make contact, please remind a friend!

Hey Drupalers!

Hey,

I've recently been put up against the huge task of scaling a large drupal site, tuning servers and the database.

Lets use this space to discuss performance issues that anyone has come up with and solutions you've found for this.

Starters for discussions:

PHP Accelerators : Which one to use and when?

Caching Techniques : Drupal Cache, Squid, Memcache

Database Optimization : MySql variables, InnoDB vs. MyISAM

Apache Tuning

What else?