Getting the max values records

Hi all, do help me...
I have a table with these fields...

id | line | header | description
= | === | ===== | =========
1 | hi | good |how are you?
2 |U | wow |how is your class?
3 |me |trouble |problem with fetching records

etc....

the id is auto incremented as and when the records are inserted. Now the problem is once, I want to fetch the record, then the id with the maximum number should be displayed. the query works fine if it is with individual statements like

select max(ad_id) as Idd from pbl_content or

select ad_id, ad_top_line, ad_header, ad_description from pbl_content.

I want to get the value of the id with the max value and once I write the coding the error coming is

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in

and my query is
select ad_top_line, ad_header, ad_description from pbl_content where ad_id=max(ad_id)

If you order the results by id descending and limit the results to 1 this should achieve that effect. Something like (this is bound to be a bit off as I have no way of testing it) -

SELECT ad_top_line, ad_header, ad_description from pbl_content ORDER BY ad_id DESC LIMIT 1

Hope this helps,

-KM-