How can I install Ubuntu without CD?
how to install ubuntu on a netbook without cd?
The easiest is to use a USB stick.
Download the Ubuntu ISO Image. Create a USB Stick with the Ubuntu Install. Install Ubuntu by booting from USB Stick when starting the Netbook.
The instructions are right there on the steps mentioned on the Ubuntu Download Page.
Since you do not give any information on your setup, I'm going to assume you have access to a Windows machine on the side.
Download unetbootin and the .ISO file for Ubuntu (or any other distro for that matter) that you want to install. Choose the USB stick and the ISO file in unetbootin and it will load it onto the USB.
When booting the netbook, look out for something like "edit boot order", "boot menu" or something similar, usually you get it by pressing F10 or some similar button. Spam press this button until you get the menu, from there choose the USB stick and the rest should be evident.