I don't know anything about Linux ??

Edited text of question.

go to www.cheapbytes.com buy redhat 6.0 cd-rom for 2.99 then use in dos mode you need to create free partition space and use ezstart to install redhat create / partition and swap

 Is Linux for free ?

Yes, Linux is free to download from anywhere you can find it (all the major distributions can be downloaded from their own FTP sites, and they often make .ISO images available for those of us with fast connects and CD-burners).  "Linux" in it's purest form is only the kernel, but often the entire OS is referred to as "Linux", since it uses the Linux kernel.  Some of the major distributions (everyone packages a little differently, so you'll have to ask around to find out which one is for you [the topic of the best distro is a VERY heated one in the Linux community and I don't want to start that all over again here]).  Below are the links to the big 4 distros:

Debian: www.debian.org
RedHat: www.redhat.com
SuSE: www.suse.com
Caldera: www.caldera.com

  So, do you know someone already asked the same question like me ? Actually, I had a CD Linux RetHat 5.0, but I don't know how to install. Can you help me ?

Assuming you have windows, dos or some other Microsoft operating system on your box now, and have access to your cdrom drive, place the Red Hat CD into the drive.  shell to a dosprompt (if you are in windows) and type "cd <cdrom-drive-letter> [enter]"...

Type DIR on the cdrom and you should see a directory titled "dosutils"...  Type "cd dosutils" and then type the command "dir rawrite.*" and a utility called rawrite.exe and rawrite.doc reside in this directory.  I copied rawrite.exe to a directory in my system's path (e.g. c:\dos or c:\windows\command) by typing "copy raw*.exe c:\<path-directory> [enter]".

On the command line go back to the c: drive and type "rawrite" and see if the program is there.

Now get a floppy a format it "format a: /q" and now cd back to the cdrom and type "cd ..\images [enter]" now do a dir command and you should see a file called "boot.img".

Everything cool, now type "rawrite" at the command prompt and the program will popup with "Enter disk image source file name:", type d:<or cdrom drive letter>\images\boot.img" and press enter.
Next it'll ask "Enter target diskette drive:" and you will type "a:" and enter.

The rawrite program then writes the bootdisk for RedHat.

Keep the floppy and the cd in your drive and then reboot your computer.

The system will boot with the Linux Kernel and press enter at the prompt.

Next it asks you language and about scsi devices, just press enter (unless you do have a scsi CD). Next it'll ask where you want to install from and you should select the CDROM option (use arrow keys, tab and enter to navigate through the installation).

After it finds the cd it'll start the kernel again and will continue the installation.

If you have installed Windows and used FDISK before, the rest should be a breeze.

Cheers,

 What do I need to do before installing Linux ? I'm using Windows 98. My hard-disk is 6GB. I had two partitions.
  I can't understand that everytime I install Linux, it always asks about something line "mount". What is it ? I couldn't pass this step.

Take JBURGHARDT's advice and go to cheapbytes and get the 6.0 version for $2.99. You do not want to use the older versions, 6.0 has the newest kernal, it is more stable than previous versions. RedHat is nearly as easy to install as Win95, but having the spec's on your PC hardware would greatly limit any chance for problems. If you do not know anything about Unix, or Linux, you are asking for the keys for a spaceship, likely to crash and burn if you are not careful. Linux is very powerful, eay to build, easier to destroy. Get a copy of Linux for Dummies to get you going, it will take you a long way. Also, subscribe the the elug (Everyones Linux Users Group) Listserv to be intouch with helpful, and knowledgable Linux users.  Send mail to majordomo@elug.org  and put SUBSCRIBE in the body of the message, or go to http://www.elug.org   

  This didn't help me. I got a problem with "mount failed". I didn't understand what it was. This step always repeat when I tried to pass.

Why would you think that it would only take one question to teach you all about Linux, not to mention how to install it.  The usual question would be,  you have tried to install Linux by reading the How Too's, or the book, and have gotten an error message which you do not understand, and you want help getting past it.

Don't expect someone to keep jumping into this question to answer every question that pops into your head, or onto your screen while you cut your teath on Linux.  That 160 points could have bought a lot of already asked questions on this same subject.

  So, What is "https://www.experts-exchange.com" for ? If you don't want this "160 points", let go away.
Thanks for coming.

  OK, it's nearly what I need. But after I finished installing, Linux asked me about "login" and "password", but I don't know. Pleaase help me. Thanks a lot.

During install you were prompted for a password which you needed to type twice (just for a check the second time).
Now if everything went right you configured LAN (Optional) and printer(optional) and then you configured your monitor and graphics card (real easy). You presumably, after reboot came to:
login:
{Here you just type "root"
and another prompt password: follows at which you then type the password you used at the end of the install.
Then you should get:
[root@localhost root]
now if you type "dir" at the prompt you will see some files in that root directory.
If you configured your monitor correctly, type "startx"
and you will be in Xwindows
If you were truly at this stage, you only have two possible further problems, monitor and graphics card misconfiguration (easy to fix) and\or mouse configuration incorrect. Lets see where you get with this advice first before this gets too long.