I'm not sure that you have to use MapPoint 2002 ? Or at least I didn't know that.

Do you have a reference as to why you have to use MapPoint 2002 Visual C++ 6 ? I would be curious to know... I thought the API's of MapPoint 2002/2004/2006 were just about identical.

Also, it looks like the Isle of Wight postcodes all begin with PO3 except Freshwater and a few others which are PO4.

See Isle of Wight postcodes - Google Search

I think just checking the postcode string would be relatively easy and straightforward compared to trying to trying to get something out of MapPoint... there are the reverse geocoding algorithms but I think that leaves you open to lots of potential for error.