Hi Dan
Following on from your post I have been in contact with Geosoft and I believe the problem has been solved.
It may seem silly but the programme was not loaded. Essentially it seems despite down loading from the link from the Geosoft web site for "Plug in For Arc GIS" it did not automatically load it from the "Geosoft Desktop Application". Further more I found that I had two different versions of "Geosoft Desktop Application" loaded. So the solution is as follows:
1. Close all Geosoft and ArcGIS programs.
2. Go to Control Panel > Programs and Features.
3. From the list of programs right-click on Geosoft Desktop Applications and select Change (Note if at this point to have two "Geosoft desktop Applications" loaded right click and uninstall the older) then right click on the new and follow the instructions below.
This will open up a Geosoft wizard
4. Select Add of Remove Applications.
5. You should already have Target 9.3.3 and Oasis Montaj Viewer 9.3.3 selected.
Can you confirm if the Plug-in for ArcGIS 9.3.3 is also selected. If not, then you just need to it and then click Add or Remove.
This will now install the programme.
Simple but probably not intuitive.
Once again thanks for you assistance.
Cheers
Mark