How to create a cumulative posts and members count

Question

I need to show my users cumulative posts and members registered count by date. It has to be displayed in an array format like this

for posts

array(array(2011,08,02), 500)
array(array(2011,08,03), 520)
array(array(2011,08,04), 540)
array(array(2011,08,05), 560)
array(array(2011,08,06), 580)

the same case for members

iam using wordpress.com stats to for statistics, i cant figure out how to do this, could anyone help me...