You can use a subquery for this like

select *
from  
( select * 
  from emp 
  order by sal desc ) 
where ROWNUM <= 5;

Have also a look at the topic On ROWNUM and limiting results at Oracle/AskTom for more information.

Update : To limit the result with both lower and upper bounds things get a bit more bloated with

select * from 
( select a.*, ROWNUM rnum from 
  ( <your_query_goes_here, with order by> ) a 
  where ROWNUM <= :MAX_ROW_TO_FETCH )
where rnum  >= :MIN_ROW_TO_FETCH;

(Copied from specified AskTom-article)

Update 2 : Starting with Oracle 12c (12.1) there is a syntax available to limit rows or start at offsets.

SELECT * 
FROM   sometable
ORDER BY name
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;

See this answer for more examples. Thanks to Krumia for the hint.