Handling Huge Data insert  and retrieval from MS SQL Server 2005

1.2 Billion records per day.. 116 billion for 90 days.. that's really huge (atleast for me!). I have not dealt with such huge data (or anywhere near to that). Okay, so you have 15000 points which will insert 1 record each per point per second.. which means 3600*24 = 86400 records per point per day, that means 7,776,000 records for 90 days. And you always query for a single Point at a time.

select REAL_VALUE, INT_QUALITY from HISTORY_DATA where INT_POINTID=9999 and INT_DATETIME>20140330145022968 and INT_DATETIME<20140403145022968

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So, I would suggest you give emphasis on PointID rather than DATETIME column. Try creating a NON-CLUSTERED index as below which should INCLUDE the columns you want to SELECT. This means your storage requirement will be double, but you may get faster results. Please try and provide your results.

CREATE NONCLUSTERED INDEX IDX_HISTORY_DATA_POINTID
ON HISTORY_DATA (INT_POINTID, INT_DATETIME)
INCLUDE (REAL_VALUE, INT_QUALITY)

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Note that you have all columns of your table in your index too, which means that your INSERT into the table may longer than before (may be even double). And if you already have 90 days of data, I am not sure how long the index creation may take.
And yes, as @ScottPletcher suggested, use "WITH (NOLOCK)" in your FROM clause (FROM HISTORY_DATA WITH (NOLOCK)).

-Harish