My machine has Windows XP SP2 installed. I want to install Ubuntu Home Edition on it. Please let me know how should I proceed without disturbing Windows XP.
You can have both XP and Linux on the same disk, by using Linux as an application within Windows. This way, you don't disturb XP at all.
I suggest the Wubi linux distribution, since it's a variant of the very popular and easy to use Ubuntu Linux:
Wubi -- an officially supported Ubuntu installer for Windows
The simplest way to check (and even use) Ubuntu installation on a USB Bootable system,
I think a USB Harddisk will also do -- all you need is your platform (PC+BIOS) should be able to boot through it (else, things get a bit more complicated).
When you boot with the Ubuntu LiveCD, the first menu will allow you to install right from the LiveCD.
As a safety measure (about the 'Advanced' part above) you could just unplug your XP harddisk cabling and leave the CD Drive wired along with the external USB harddisk to boot and install.
If you are taking this last step too, you do not need to backup your XP (assuming you do not break the disk in the cable work involved) and, you can throwaway the Ubuntu installation without any impact to the XP later (just unplug the drive, format it, etc).
Further, you can also boot this Ubuntu installation on any other PC that will allow you to boot through that USB drive!
USB Drive based Ubuntu installation is my preferred way of suggesting an Ubuntu try-out on any system.
As stated: install another hard drive and put Ubuntu on that.
If you're willing to disturb XP a little, you can use the Ubuntu installer to shrink the XP partition and install Ubuntu on the same hard disk. It's actually very easy, just follow the prompts in the installer.
Note: ALWAYS back up before doing any kind of OS install!
Wubi (as mentioned by UK) is a very simple way. The downside is that it is inside the Windows partition so that if the Windows partition breaks and is inaccessible, then Ubuntu may fail too.
If you want Ubuntu as a dual boot, mainly as insurance- to know that you can get to your Windows files if Windows will not boot- then it is usually fairly easy. Lifehacker- dual boot has a guide for Windows 7 and Ubuntu, most of the information will apply to XP. Note that XP does not have a partitioning faciliity so you will need to use the GParted tool explained.
If you are looking to experiment and learn, then go with Wubu, or a Portable Ubuntu Lifehacker- Portable Ubuntu tutorial
Hope all this helps, if you need more info, shout up and let us know how far you get, what needs more explaining...