This is a tutorial to help people set up a dual boot system with both Linux and Windows. It shows how to set up the Ubuntu operating system, which is an easy-to-use GNU/Linux distribution.
Before you install Ubuntu, make sure you have your Windows disk in case something goes wrong. If Windows came with your PC, call Dell or whatever company manufactured it and ask them to ship you a backup Windows disk. Also, be sure to backup any important documents to a CD in case you mess up and overwrite your Windows partition.
Download the Ubuntu install CD and burn it using an ISO burner like ISO recorder. Do not just burn this ISO file directly as a normal file because it will not work. There are actually two install CDs: a graphical "Desktop" install CD, which also allows you to try Ubuntu from the disk, as well as a textual "alternate" install CD which requires less memory and does not allow you to run Ubuntu from the disk as a "Live CD" but is basically the same as the graphical install CD in the installation procedure.
Defragment the drive (on Windows XP click Start > Programs > Accessories > System Tools > Disk Defragmenter and then run chkdsk (open a command prompt and type "chkdsk /f"). chkdsk is a program which checks the file system for errors and fixes them. Then boot from the Ubuntu CD. You should now see the Ubuntu logo and a list of options starting with "Install Ubuntu". Press enter to select the option to "Install Ubuntu".
You should be asked some questions about language, time zone, keyboard layout, etc. These questions should be pretty self-explanitory. Ubuntu may also attempt to configure the network device. If you are on a laptop and can't plug into an ethernet cable, then just click "do not configure the network at this time."
After you answer the easy questions, you will be asked "How do you want to partition the disk ?". If you want to stop using Windows completely and just use Ubuntu (WARNING: DO NOT DO THIS UNLESS YOU HAVE BACKED UP YOUR FILES), choose "Guided entire disk" There should also be an option to "resize partition and use free space". Select that one and make the Ubuntu partition as large or small as you want. If there is no such option, there might be one to "Use largest contiguous free space". If you have already partitioned your disk using another partition editor like gparted, then choose that one to make use of the free space you created at the end of the disk. Otherwise, choose to "Manually partition disk". You should see a list of partitions on the disk. Choose that largest partition. There should be a menu with an option to "resize partiton". Type in the new size for the Windows partiton. There will now be some free space for Ubuntu. Now go to "Guided partitioning" and select "use largest contiguous free space". Continue through the installation.
When you reboot your computer, you should have a menu where you can choose Ubuntu or Windows. You can now boot into Ubuntu and log on with the username and password you chose during installation.
If you get an error paritioning your disk with the partitioner that is built in to the Ubuntu CD, download the gparted CD and boot from it. Then try partitioning using it. If it works, then boot from the Ubuntu disk and install. Otherwise, you could try running chkdsk again or asking questions here about installing.
There are other ways to install Linux other than using an install CD. Knoppix is a Linux distribution that runs directly off the CD, allowing you to use Linux without affecting your hard disk. You can also purchase a computer which comes with Ubuntu from Dell. You can also download the Windows-based Ubuntu installer which allows you to set up a dual-boot without partitioning your hard drive, or the network-based Debian installer, which allows you to install Debian without burning an ISO.