I'm new to Ubuntu. I want to install and try learning it. Do I need to format my PC and create another partition on my hard disk? I only have one partition C: and I don't want to format the PC and lose any data. Can I install Ubuntu on the same drive or partition that Windows is installed on (without uninstalling windows)?
As others have pointed out, there are many ways to install Ubuntu. The first step is to download the ubuntu-12.04-desktop-i386.iso file, as you have done. Next you have to burn that file into a CD. The instructions are at:
As it says in this page you can try using Ubuntu without installing by booting from the CD you created. This CD can also be used to install Ubuntu INSIDE windows. This method is often called Wubi installation. Ubuntu will reside in a big file in your C: drive. No new partition will be created. Neither will the C: drive be formatted. Once Ubuntu is installed you will have the choice of booting Windows or Ubuntu when you start the computer. To do this kind of install insert the CD while windows is running and follow the instructions. You can read about Wubi here:
Hope this helps.
In that case best option for your is try Ubuntu in a virtual environment. It's not possible to install Ubuntu in the same where windows is present. You need to have different partition to get Ubuntu installed. I will suggest to check out Virtual Box and give Ubuntu a spin.
Yes, you can install Ubuntu on the same hard drive as windows.
How much space do you have left on C drive?
From the Ubuntu installation menu you need to select 'install alongside windows'.
I recommend defragmenting your C drive first, although it is not necessary.
Then have a look at this guide on my personal website for details on using your BIOS to boot your installation CD / USB.