to_json in Rails 2.0.2 not generating proper json?

I am using Rails 2.0.2 and trying to use to_json to generate json. I notice several problems.

1) datetime field such as created_at mapped to "created_at": {} 2) :except does not work, @post.to_json(:except => [:created_at, :updated_at] still gives me "created_at": {}, "update_at": {} 3) problem with escaped char mapping: '<' mapped to '\074' instead of '\u003C'

Is there problem with my installation? Is there a module I should turn on? Do I need jsonifier plugin?

Help please! victor