>SQL 2012 makes it quite easy:
GREAT query...that's a great example of the new ROWS UNBOUNDED PRECEDING to get cumulative sums.
I've used this as a training example, though I also use CROSS APPLY for situations before SQL 2012. I'll wait to see if anyone wants to try an example pre-SQL 2012, and then I'll post some solutions (with yours as one of them).
Thanks, Naomi,