I'm using the latest 4.5.2 bugfixed ZCO on winxp and office 2003. So far so good, except for one user. I setup his account, it looked good. Outlook created 'outbox1' as his outbox.
Sometimes, when he sends emails, they don't get sent. They'll just hand around the outbox. When he restarts outlook then it'll get sent. Also, his sent email has problems syncing.