select and calculate

I hope this gives you the idea of what is needed

-- test table to work on
DECLARE @Table TABLE
    (
      myID INT IDENTITY ,
      myVal DECIMAL(6, 2)
    )

-- random test data
INSERT  INTO @table
        ( myVal
        )
        SELECT TOP ( 100 )
            CONVERT(DECIMAL(6, 2), ABS(CHECKSUM(NEWID())) % 20.0 + 1)
        FROM
            sys.all_columns ac1
        CROSS JOIN sys.all_columns ac2 ;

-- list the test data
SELECT
    *
FROM
    @Table AS t

-- join table to itself with an offset of 1 implemented in the JOIN
SELECT
    [t].myId AS [Record ID] ,
    [t].[myVal] AS [Record Value] ,
    ISNULL([t2].[myVal], 0) AS [Prev Record Value] ,
    [t2].[myVal] - [t].[myVal] AS [Current minus prev]
FROM
    @Table AS t
JOIN 
    @Table AS t2
ON  [t].[myID] = [t2].[myID] + 1

A horrible RBAR cte solution........

declare @YourTable table (
    [Date] datetime,
    Fread int,
    Sread int,
    Thread int,
    Fread2 int)

insert into @YourTable select '1 july 2011 00:00',18,0,31,275
insert into @YourTable select '1 july 2011 00:15',25,0,37,282
insert into @YourTable select '1 july 2011 00:30',27,0,41,293
insert into @YourTable select '1 july 2011 00:45',29,0,49,298

;with cte as (
select  row_number() over (order by date) as rownum, 
         Date, Fread, Sread, Thread,Fread2 
from @YourTable
)

select
    date,
    isnull(Fread - (select Fread from cte c2 where c2.rownum = c1.rownum - 1),0) as Fread,
    isnull(Sread - (select Sread from cte c2 where c2.rownum = c1.rownum - 1),0) as Sread,
    isnull(Thread - (select Thread from cte c2 where c2.rownum = c1.rownum - 1),0) as Thread,
    isnull(Fread2 - (select Fread2 from cte c2 where c2.rownum = c1.rownum - 1),0) as Fread2

from cte c1

This doesn't help you right now, but I just want to give you something to wait for.

In the next version of SQL server (Denali) you would be able to calculate this with OVER clause like this, without any CTE, RBAR or cursor solutions:

SELECT 
[ProductID]
,[StartDate]
,[EndDate]
,[ListPrice]
,SUM([ListPrice]) OVER(Partition BY ProductID ORDER BY ModifiedDate ROWS BETWEEN 1 PRECEDING AND CURRENT ROW)
,[ModifiedDate]
FROM [Production].[ProductListPriceHistory]

Clean and simple! :) If you like to try it, download CTP3 of Denali.