Sort And Select, Which Executes First?

I use SQL Server 2005.

I want to split the data in a table into two parts, say 30%-70%.

Here are my query statements:

-- 30%

SELECT top 30 percent * FROM DataTable ORDER BY Col1

--70%

SELECT top 70 percent * FROM DataTable ORDER BY Col1 DESC

Somebody says the result is not guaranteed to be correct since in SQL Server 2005, the query optimizer may choose different strategy to execute the query statement.

I think select should execute after order by, which has nothing to do with query optimization. Am I correct?