Subquery To Find Previous Value

I have created this sub query:

Code:
(SELECT SUM(Cash)
FROM qryAccountSetup AS T2
WHERE T2.ClientID = [qryAccountSetup].ClientID
AND T2.MonthlyDate < [qryAccountSetup].MonthlyDate) AS PriorCash,

How do you change this to allow multiple values. I looked up subqueries online and it said to nest a second sub for the where clause....

Code:
(SELECT (Cash)
FROM qryAccountSetup AS T2
WHERE
(Select (SELECT MAX(T3.MonthlyDate)
FROM qryAccountSetup AS T3
WHERE T3.ClientID = qryAccountSetup.ClientID
AND T3.MonthlyDate < qryAccountSetup.MonthlyDate)) AS PriorCash,
But i keep getting error.

What i am trying to do is get the previous cash value.... For now, a good indicator is MonthlyDate, as only one date per client will exist. Something can only happen once in a day....IE.

ClientID..MonthlyDAte
1...........03/01/2013
1...........31/01/2013
1...........01/02/2013
1...........and so on.

There can be multiple dates, however the clientID would not match then.... Does this make sense? There is also a PositionID... This is an autonumber field in its respective table.. I have that so i can use it for domain purposes in the future.