Does this work?

-- 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