oh dear...help

I started off with the best of intentions. Every time I added photos to iPhoto I would put them into an album and add comments and keywords. However, gradually, over the last year or so, I have stopped doing this, and as our collection has grown, it became a bigger and bigger job. Adding to this problem is that, for some reason, I seem to have about a thousand duplicate photos. They're not straight forward duplicates though. iPhoto seems to have ignored the metadata and decided to store them in strange places. For example, photos taken on 26.07.02, our wedding day, are stored in iPhoto Library > 2002 > 07 > 26, which seems simple enough. But, I also have some of the same photos stored in 2001 > 07 > 26 and 2004 > 02 > 19, and in other places too. It is just a little bit odd. Oh, and the thumbnails that Finder uses seem to have become mixed up with the full-size pictures too. I have tried a variety of methods and tools to try to sort it out, but without luck. iPhoto is a great app, and it usually creates a very neat database, leaving to one side it's reluctance to throw anything away...Ah, the penny has just dropped. The huge number of duplicates probably has something to do with iPhoto's insistence on making copies every time you change something, but that doesn't explain why it would be changing where it stores the information. I wonder if it has something to do with reimporting the library, which I have had to do on a regular basis over the years because I am forever messing up my OS install. The truth is I just don't know what is going on. Fortunately, I have quite a few of the photos on disc somewhere, so I might just start again. Although, I can't bear the thought of having to go through the library picking out the photos that I want to keep.

Does any clever soul out there have any idea how to sort this out with the minimum of work?