Hi Murray,
congratulations on your job and you will find one day that something from your MSc does prove useful! I know in ArcGIS10, a simple right click on the layer will provide you with options including a Data tab and under that repair data sources will usually repair all the layers in the MXD if they are in the same directory. I am pretty sure that similar functionality is in 9.3.1 but I don't have an instance of that in front of me to confirm.
Cheers
Len