Number sequencing problems !!!

[hopeless]

Hi,
Please can anyone help? Beleive me I've tried for hours already!

I list on a book selling website which allows me to post 5 photos of each book. So for every ten books I shoot 50 photos (5 of each book!) which are naturally recorded sequentially on my camera as Dsc07900, dsc07911, dsc07912 ....all the way to dsc07950.

I am on book 1500 at the moment and my jpegs must take take the form of :-
001500_1 , 001500_2 , 001500_3 , 001500_4 , 001500_5.... then for the next book listing :-

001501_1 , 001501_2 , 001501_3 , 001501_4 , 001501_5, next book listing etc.

So I figure there's two separate number sequencing problems to work out here - is it possible to get anywhere near automating this process?