How to write JavaScript in post, WordPress 2.0

1. Turn off tinyMCE

Users -> Your Profile and then scroll all the way down and uncheck the Use … box.

http://wordpress.org/support/topic/56563

2. Use the Text Control Plugin, and choose No Formatting for the post that want include javascript.

If you are having trouble with including Javascripts inside a post, use the Text Control Plugin which allows you to control on a global or per post basis the ability to turn off WordPress’ automatic formatting features which can quickly turn code into something readable instead of executable. Set the options on the post that you will be using the Javascript on to have No Formatting or Markup or nl2br and No Character Formatting. You may have to experiment to get it to work. As a reminder, when using the Text Control Plugin, you must first Save and Continue Editing the post in order to see the Text Control Plugin options.

If you choose No Formatting, your post’s text will run together, so you will have to add paragraph tags and other HTML tags in order to format your page as WordPress normally does that for you.

http://codex.wordpress.org/Using_Javascript