It should fit just fine as they are the same frame and fuel tank as far as I know.
Here's a funny thing about the 2005 Tiger I had before I got the new Tiger 800:
I had owned the '05 for about 2 years and just couldn't get quite comfortable on it. As I was cleaning it up/detailing it for sale because I had a buyer coming to look at it, only then did I discover that the seat could be adjusted for height. The entire time I rode it the seat was in the highest setting! No wonder it didn't feel like my buddy's 2002 Tiger.
That'll teach me to read the whole f'n manual, which I did with every other bike I've owned before and after!