My CD drive is broken,so I can't install Ubuntu from a CD.
Are there any workarounds for that?
There are several options for installing without a CD drive.
If you have Windows installed already, you can use Wubi. Wubi installs Ubuntu as an application inside Windows.
Alternatively, you can also install Ubuntu from a USB disc. You'll need a USB flash drive, and Ubuntu live CD ISO, and a program to transfer it to the flash drive.
Making a USB startup drive
If you have Ubuntu installed, you can use the Ubuntu USB Creator, which is in the System > Administration menu.
If you only have Windows installed, you can use Unetbootin to do the same job.
Booting the drive
Once you have a bootable USB drive, you simply have to plug it in and during bootup specify it as the boot device. There are instructions on the Ubuntu wiki On how to boot from a USB drive. Once it's booted, it acts just like a live CD.
Wubi will allow you to install Ubuntu while keeping Windows installed. If at anytime you decides he does not like Ubuntu you can uninstall it just like a normal program and it will give him his space back. If you does any other install it will be much harder to uninstall. You'll have to use the Disk Management tool and delete the partition and then extend the Windows partition. In order to get Wubi you can download it at http://wubi-installer.org/ or download the current Ubuntu release and then use 7-Zip to extract the ISO and then click on wubi.exe. An installer should appear and he can follow the instructions from there. It's very simple for even the most non-tech users.
I am using Unetbootin in order to create a bootable USB.