Summarize date values

Hi,

I have a dataset containing dates in the A coloumn and values in the B coloumn.
I have several values for the same date, example:

A B
1/1/2010 2000
1/1/2010 -500
1/1/2010 -200

I want to create a line chart, where the the net value of each date represents the starting point for each date.
Can excel summerize the net value of each date so this is possible?

Appreciate all help immensly

Gnoke