LOOKUP value by finding specific date

Please see spread sheet attached.

I want to look up in column A the date that chronologically matches up to the row in question. Once I find this correct row, I want to pull the cumulative balance in column S.

Man - I should know this... driving me nuts!

Anyone have any bright ideas ?

Still stuck - please let me know if my explanation / example spread-sheet is not clear. I will put a small video explanation together if need be?

Sorry for the slight spamming here but I have put together this 2 minute video

Video: http://screencast.com/t/6oo1FlDIf3w

This along with the example spread-sheet should help explain to those that can help, what exactly I am looking at achieving.

Thanks in advance to anyone that can assist me!

If anyone could let me know if what I am requesting is too difficult / doesn't make sense I will revise my explanation?

More simplistically put: How can I use a date to look up Column A and find where my date would be chronologically?

If I know this I can pull a corresponding value from the row I am interested in...