I have one operating system installed on my pc
I want to uninstall it and install linux
How should I start?

First pick a Linux distro
For the NEW Linux user i would recommend installing Ubuntu
Ubuntu is targeted towards the new *nix user and is very user friendly

just Google Ubuntu and " installing Ubuntu "

This is the easiest way to install Linux. For most or all of the more popular versions, the installer will automatically do all of the required partitioning, etc.

Ubuntu is certainly a good choice. Other good options can be found at http://distrowatch.com Anything in the top 5-10 on their "hit list" should be fine.

Good luck and welcome to LQ!!

I would recommend Ubuntu also. It is the best of the "beginner friendly" distros in my opinion.
If you are currently using Windows, you do not have to remove Windows to install linux. You can set up a dual boot system. This will allow you to choose whether you want to boot linux or Windows when you start your computer. I have Ubuntu, Slackware, and Windows XP on the computer I am using now.

Here are 2 great websites for getting started with Ubuntu, and setting it up as a dual boot system:
http://www.psychocats.net/ubuntu/
http://members.iinet.net/~herman546/
Of course, you can also remove Windows if you want to and use only linux. It is your choice. Linux is all about freedom of choice.

And welcome to the LQ forums!!!

You don't have to do anything specific about uninstalling your old OS; if you tell your new OS to use the space ( = the same partitions on your disk) as your old OS, it will reformat those partitions (= overwrite the data) and set up the boot arrangement for you.

Given that this will overwrite your existing data, ensure that you have copied all of the existing data that you have and want to keep. Preferably always have one more copy than you think that you need...

And live CDS are a good thing; with a live CD you can have a 'no commitment' trial of your new OS before you finally decide to install. Very handy if you want to compare two or more versions before making a final decision.

As Salasi said, make sure you back up some of the data that you want on linux, such as movies, music, documents, etc. You don't want to have get all that back again!