How did you already know, Ubuntu (Natty Narwhal) does not permit to add widget in the desktop. At least, for Memory, CPU, Network and Hard disk there is a solution that permit us to track in desktop. It’s called Indicator Multiload.
To install it, open a terminal and run:
sudo add-apt-repository ppa:indicator-multiload/stable-daily
sudo apt-get update
sudo apt-get install indicator-multiload
Now, press Super and type:
System Load Indicator
After that, click on the icon to start the application.
That’s it. More information you can get in www.webupd8.org.
See you next time.