set nocount on

--Set up your Table
set dateformat 'dmy'
declare @t table ([id] int, [start] datetime, [end] datetime)
insert @t 
select 1,'01/01/08 13:00:00', '03/01/08 13:00:00'

--set up a table of Integers (starting with 0)
declare @numbers table (number int)
insert @numbers select number from master..spt_values where type = 'p'


select d.id
       ,case 
              when n.number = 0 then d.[start]
              else dateadd(day, n.number, dateadd(day, datediff(day, 0, d.[start]), 0))
              end as [start]
       ,case
              when d.SplitCount = 0 then [end]
              when n.number = 0 then dateadd(minute, datediff(minute, d.[start], d.startDayEnd)-1, d.[start])
              when n.number < d.SplitCount then dateadd(minute, n.number*1439, d.startDayEnd)
              else d.[end]
              end as [end]
from   (
       select t.id
              ,t.[start]  
              ,t.[end]
              ,dateadd(day, 1, datediff(day, 0, t.[start]))    startDayEnd
              ,dateadd(day, 0, datediff(day, 0, t.[end]))      endDayStart
              ,datediff(day, t.[start], t.[end])               SplitCount
       from   @t t
       ) d
inner join   @numbers n
       on  n.number <= d.SplitCount


OUTPUT:
id          start                   end
----------- ----------------------- -----------------------
1           2008-01-01 13:00:00.000 2008-01-01 23:59:00.000
1           2008-01-02 00:00:00.000 2008-01-02 23:59:00.000
1           2008-01-03 00:00:00.000 2008-01-03 13:00:00.000