If the default hibernate does not work on your Ubuntu installation, try installing the package hibernate.
sudo apt-get install hibernate
To use that script then, you can run it via the terminal
or create a shortcut on your panel, right-click and Add To Panel, then select Custom Application Launcher and set it up as follows:
After you click Add, there will be a new icon added to your Panel.
Note: when you run the newly created icon it will ask for a password because you are executing it with sudo.
This is tested on ASUS K53SV with Ubuntu 11.04.