-- first, some setup.

CREATE TABLE #Amounts (
 SomeDate DATETIME,
 SomeAmount INT
)

insert into #Amounts values ('2008/09/01',500)
insert into #Amounts values ('2008/09/02',1500)
insert into #Amounts values ('2008/09/03',3500)

-- Setup finished


CREATE TABLE #WorkTable (
	RowID INT IDENTITY PRIMARY KEY,
	SomeDate DATETIME,
	SomeAmount INT
)

INSERT INTO #WorkTable (SomeDate, SomeAmount)
SELECT SomeDate, SomeAmount
	FROM #Amounts
	ORDER BY SomeDate
	
SELECT CurrentDay.SomeDate, CurrentDay.SomeAmount-PreviousDay.SomeAmount from #WorkTable PreviousDay inner join #WorkTable CurrentDay
	on PreviousDay.RowID = CurrentDay.RowID - 1

We walk in the dark places no others will enter
We stand on the bridge and no one may pass