1. Start PC
2. Open CD-ROM or DVD-ROM
3. Place Disk in tray
4. Close Tray
5. Hit enter at Grub screen
6. When desktop shows on desktop double click the install icon
7. Answer questions
8. Wait patiently for 15 to 30 minutes depending on your computer speed
9. when its done click on restart your computer
10. When rebooted eject CD-ROM/DVD-ROM tray. remove disk
11. Let PC/OS boot
12. Enter user name and password
13. Enjoy.

It's never quite as simple as suggested above.

Firstly it is perhaps better to have a second hard drive on which to install PC-OS. An empty one.

If you just have one hard drive then the automatic option is to use the largest free space and make that into partitions for the linux installation. The problem with that is what happens to Windows XP. Your main operating system now has a shortage of space because you just used up all of it's free space to put another operating system on the same drive.

The above list is not literally correct.
You turn the computer on and let it start up so that you can open the optical drive.
When you put the disc in Windows XP (or what ever) will try to open it. You can let it or not as you choose.
Then you will restart and the assumption here is that the computer will start up on the CD or DVD ROM.

It might not do that. If it doesn't it's because the BIOS needs to be changed so that the computer checks as it starts up to see if there is a disc in the optical drive. It might not be set to do that. To get to the BIOS (if you have to) the usual thing is to hit the 'Del/Decimal Point' button on the numeric keypad when the motherboard logo apears on the screen (ASUS). Then you have to be very careful to change the Boot Order so that the CD-ROM is first on the list with the main hard drive as second. Then usually it's F10 to save the setting and restart.

The rest here is correct. The result writes what is known as a Grub loader into the MBR (Master Boot Record) of the hard drive and this gives you a menu choice of whether to start up with PC/OS or Windows XP (say). This is probably a good thing but the Grub loader is very difficult to get rid of if you change your mind later on.

If you have a second hard drive and don't want the grub loader messing up your first hard drive you might try a more advanced approach.

In my case with two hard drives, this is what I did:
As the computer starts up hit del and get to the BIOS settings for the motherboard, in this case an ASUS P5B.
Set the BIOS so that the empty hard drive is the 1st hard drive and then set it as the one to boot up on.
F10 to save and restart and it tries to restart on the empty hard drive.
Press and hold the power button until it shuts down, or wait to see if it will try the other drive, if so let it and then shut down.
Open the case and pull the SATA plug of the first hard drive where it's plugged into the motherboard.
Restart the machine and as soon as the optical drive light, lights up press the button and put the PC/OS disc in quick.
After it boots up on the disc install PC/OS, and make sure it starts up OK.
Shut down and plug the main drive SATA plug back into the motherboard.
Close up the PC case.
Restart and hit del again as it starts up.
Reset the BIOS to have the main hard drive as the 1st drive and then set that as the boot drive.

* By switching these settings you can choose which operating system starts up by default.

The computer will start up normally on Windows XP, but if you want PC/OS instead then when you hit the ASUS logo page, you press the F8 button twice and wait. Eventually you get a list of possible drives to boot up from. You select the other drive, hit enter/return and the machine starts up on that drive instead.

The end result is two separate hard drives that can both be backed up separately if required, without the grub loader contaminating the first hard drives MBR. This appears to work well, it gives access to both while maintaining XP as the master operating system until such a time as you want it the other way around, in which case just adjust the BIOS again.

With Vista:
If you have Vista you should make a partition first (after doing a backup of the drive in case it goes wrong) on the main drive. The way to do this is by using the Adminstrative Tools in the Control Panel:

Start > Control Panel, Administrative Tools, Computer Management, Storage, Disk Management
Click on the main drive partition and then Action > All Tasks > Shrink Volume.

It will tell you how much you can shrink it by (but don't go all the way). You would then use the remaining unallocated area to create a new partition leaving about 500MB unallocated as breathing space (for Vista's miscalculations about how big it's partition is). This new partition is what you would then select as the place to install PC/OS. So try to remember how big it is and what the brand of the hard drive is, so you can identify it more easily during installation.

This way you can share space between Vista and Linux on the hard drive so that both have enough room.

* Don't just install, think about it first!