Sql Server 2005 no tiene la sintaxis límite que tiene arriba, que no se agregó hasta 2012. Querrá usar la cláusula OVER y las expresiones de tabla comunes.
WITH Members AS
(
SELECT M_NAME, M_POSTS, M_LASTPOSTDATE, M_LASTHEREDATE, M_DATE, M_COUNTRY,
ROW_NUMBER() OVER (ORDER BY M_POSTS DESC) AS RowNumber
FROM dbo.FORUM_MEMBERS
)
SELECT RowNumber, M_NAME, M_POSTS, M_LASTPOSTDATE, M_LASTHEREDATE, M_DATE, M_COUNTRY
FROM Members
WHERE RowNumber BETWEEN 1 AND 20
ORDER BY RowNumber ASC;