How can I find Unicode/non-ASCII characters in an NTEXT field in a SQL Server 2005 table?

I have a table with a couple thousand rows. The description and summary fields are NTEXT, and sometimes have non-ASCII chars in them. How can I locate all of the rows with non ASCII characters?

I have sometimes been using this "cast" statement to find "strange" chars

select 
    *
from 
    <Table>
where 
    <Field> != cast(<Field> as varchar(1000))

First build a string with all the characters you're not interested in (the example uses the 0x20 - 0x7F range, or 7 bits without the control characters.) Each character is prefixed with |, for use in the escape clause later.

-- Start with tab, line feed, carriage return
declare @str varchar(1024)
set @str = '|' + char(9) + '|' + char(10) + '|' + char(13)

-- Add all normal ASCII characters (32 -> 127)
declare @i int
set @i = 32
while @i <= 127
    begin
    -- Uses | to escape, could be any character
    set @str = @str + '|' + char(@i)
    set @i = @i + 1
    end

The next snippet searches for any character that is not in the list. The % matches 0 or more characters. The [] matches one of the characters inside the [], for example [abc] would match either a, b or c. The ^ negates the list, for example [^abc] would match anything that's not a, b, or c.

select *
from yourtable
where yourfield like '%[^' + @str + ']%' escape '|'

The escape character is required because otherwise searching for characters like ], % or _ would mess up the LIKE expression.

Hope this is useful, and thanks to JohnFX's comment on the other answer.