--> Test Data: @T
declare @T table (id int identity(1,1), [c1] int,[c2] numeric(21,0),[c3] datetime,[c4] datetime)
insert into @T
select 888000,919633574558315468750,'2008-09-19 21:17:11.547',null union all
select 888000,919633574558400156250,'2008-09-19 21:17:20.017','2008-09-19 21:17:20.017' union all
select 888000,919633574560137812500,'2008-09-19 21:20:13.780','2008-09-19 21:20:13.780' union all
select 888000,919633574560213750000,'2008-09-19 21:20:21.377','2008-09-19 21:20:21.377' union all
select 888000,919633574560485937500,'2008-09-19 21:20:48.593','2008-09-19 21:20:48.593'

select * from @T
--Code
select c1=
case 
when exists(select 1 from @T where c1 = a.c1 and id < a.id) then '' 
else ltrim(c1) 
end,
c2,c3,c4 from @T a
--Drop

--Result
/*
c1           c2                                      c3                      c4
------------ --------------------------------------- ----------------------- -----------------------
888000       919633574558315468750                   2008-09-19 21:17:11.547 NULL
             919633574558400156250                   2008-09-19 21:17:20.017 2008-09-19 21:17:20.017
             919633574560137812500                   2008-09-19 21:20:13.780 2008-09-19 21:20:13.780
             919633574560213750000                   2008-09-19 21:20:21.377 2008-09-19 21:20:21.377
             919633574560485937500                   2008-09-19 21:20:48.593 2008-09-19 21:20:48.593
*/