Do you happen to have MS Desktop Search installed as there have been some topics raised about that and outlook 2003, so not sure if that might have any effect on office 2003.
You could enable 'Show detailed info on performed action' in standard shield to see exactly what is being scanned when you open an office doc.
Have (or did) you have another AV installed in this system, if so what and how did you get rid of it ?
Or do you have any other security software anti-spyware/adware, etc. that could result in double scanning ?
Other than this I can't think of anything that might slow the opening. How long do they take, what was it previously, what happens if you pause standard shield ?