CREATE TABLE [dbo].[BigTable]
(
    [TimeKey] [int] NOT NULL, 
    [SegmentID] [int] NOT NULL,
    [MyVal] [tinyint] NOT NULL
) ON [BigTablePS1] (TimeKey) -- see below for partition scheme

alter table [dbo].[BigTable] add constraint [PK_BigTable] 
primary key (timekey asc, SegmentID asc)

-- will evaluate whether this one is needed, my thinking is yes 
-- based on the expected select queries.
create index NCI_SegmentID on BigTable(SegmentID asc)

-- fetch just one particular row...
select MyVal from BigTable 
where TimeKey=5555 and SegmentID=234234

--fetch for a certain set of SegmentID and a particular time...
select 
   b.SegmentID
  ,b.MyVal 
from BigTable b 
join OtherTable t on t.SegmentID=b.SegmentID
where b.TimeKey=5555 
  and t.SomeColumn='SomeValue'

update t
set t.MyVal=p.MyVal
from BigTable t
join #myTempTable p on t.TimeKey=p.TimeKey 
                   and t.SegmentId=p.SegmentId

CREATE PARTITION FUNCTION [BigTableRangePF1] (int)
AS RANGE LEFT FOR VALUES 
(
   3680640 +   0*1440, -- 3680640 is the number of minutes between 2001/01/01 and 2008/01/01
   3680640 +   1*1440,
   3680640 +   2*1440,
   3680640 +   3*1440,
   ...snip...
   3680640 + 363*1440,
   3680640 + 364*1440,
   3680640 + 365*1440
);
GO

CREATE PARTITION SCHEME [BigTablePS1]
AS PARTITION [BigTableRangePF1] 
TO 
(
    [PRIMARY],[PRIMARY],[PRIMARY],
	...snip...
    [PRIMARY],[PRIMARY],[PRIMARY]
);
GO