We're just ironing out the final details here, I hope to have a formal update available by COB today.
In the simplest terms, there are certain circumstances where specific archived items will not be available to end users running the EV Add-in and Outlook 2003 SP3.
The items affected contain either a large number of recipients or a large number of attachments.
I can say for sure that, short term at least, we won't be supporting the use of Outlook 2003 SP3 on the Enterprise Vault server itself.
I'll update this post a little later on today with the official details.
Thanks!
Ian