Phil,
tricks is right. It's digit 12 in the VIN, so on an 05 model it should look like:
...249SC500....
Actually there haven't been many changes between 2003 and 2008.
The majoor ones I'm aware of are
1) different rear shocks
2) slightly improved forks
3) they slightly moved the footpegs towards the rear end (I think in 2006 and only about half an inch)
4) angled/later(2005?) straight sump guard
4) There are also some minor changes like different brake disc protectors, but other than that, it's manly different paintwork schemes.
Have a look at the following website. I found it quite helpful in order to help distinguishing different models.
http://utahtrials.com/bike_pics/scorpa/scorpa.html
Basically the changes are:
2003 fuel tank blue, frame black, rear fender white, rims uncoated alloy
2004 fuel tank blue, frame blue, rear fender white, rims uncoated alloy
2005 fuel tank grey/black, frame silver, rear fender white, rims uncoated alloy
2006 fuel tank blue, frame silver, rear fender white, rims black, TiN forks
2007 fuel tank blue/grey/white, frame medium grey, rear fender blue, rims black, TiN forks
2008 fuel tank white/light blue, frame black, rear fender white, rims black, TiN forks
Hope this helps.
Cheers Wolf