Excel 2003 SP2

Trying for format a cell based on the sum of a range in which the cell
exists versus amount in another cell.  So if the number in the cell changes,
making the total of the cells exceeds a predetermined number, then the cell
should be red.  In verbal logic: if sum(a1:a10)>B1 then format A2 red.

Can this be done through conditional formatting, or do i need to write a
change-cell event code?

Thanks.