SUM using string tag as start point

[chaz]

Data looks like this:

DATE AMOUNT
23-Sep-06 $1000.00
29-sep-06 $1500.00
06-Oct-06 BASE
12-Oct-06 $1200.00
16-Oct-06 $1425.00
. . .

I want to sum all the values in the AMOUNT column from the cell following the "BASE" entry to the end of the column.

My initial attempt: SUM(IF($A:$A > LOOKUP("BASE",$B:$B,$A:$A),$B:$B ))
The thought being to find the date of the "BASE" entry and sum all of the values with a date greater than that.

I need to be able to move the "BASE" entry around and have the sum automatically work.
Also I need to be able to add rows of data and have the formula automatically work.

Any ideas greatly appreciated.
-chaz