Chatter message history

Hello guys

I want to use Apex code to search the chatter history.

I find a standard object "ChatterMessage " at below link, but when I get some search it has an error.

http://www.salesforce.com/us/developer/docs/api/Content/sforce_api_objects_chattermessage.htm

And I'm also unable to edit the "Manage Chatter Messages" permission on my System Administrator profile, should this be so? Could anybody can help me about this?

String userid='00590000000laxMAAQ';
String str = 'SELECT Body, ConversationId, SentDate FROM ChatterMessage WHERE SenderId= :userid';
LIST<SObject> L = Database.query(str);

EXCEPTION: System.QueryException: sObject type 'ChatterMessage' is not supported.
STACKTRACE: AnonymousBlock: line 3, column 1
LINE: 3 COLUMN: 1