I have an iMac A1224 with Xp Installed, but I need to make a clean installation of windows XP, how can I start the installation

Well since you already have a partition set for XP, all you have to do is pop in the XP disc and do what you usually do. Meaning that you put the disc in, go through all the XP installation stuff, make sure you choose to format the XP partition and not your OS X partition then follow the installation steps. Once you are done, just choose to boot up from XP.

The system does not read the Installation CD on Startup, do I have to press on any key to choose to boot from CD

When I turn on the system, a white screen appears for few seconds then the system goes on XP, how to make it boot from cd rom

Hold the C key as the iMac restarts. That should force it to try booting from the Windows installer disk.
If this is a wipe and reinstall of XP, you could also use your Boot Camp utility to remove the Windows partition completely, then just set it up again.

Holding the C key does not resolve, what is the boot camp utility?

how can I make my system boot from cd rom,

how can I change my boot priority?

In Mac OS X side, go to System Preferences > System > Startup Disk, and drag the system you want as first on list.
In Windows side, there should be something similar in Control Panel.

When booting the Mac, hold down ALT (or option) key, and you can select where to boot - which bootable system and/or optical disc if inserted.

Boot Camp is on your iMac hard drive, in Applications, then Utilities. Look for 'Boot Camp Assistant'
When you run the Boot Camp utility, and your Windows partition already exists, Boot Camp will ask you if you want to remove that partition. The only way that will work is if that Windows partition was originally created by the Boot Camp utility.
If no Windows partition exists, Boot Camp will ask if you want to create one.

If you get confused by the Startup Disk pref pane - there's not a list, but there are icons for each bootable partition. Just click on the one you want to choose as the Startup partition/disk

You have been of a great help,
It works, I booted from CD and started my XP Installation but when the system restart, it tells me that the File "Windows root>\system32\hal.dll" is missing,
what could be the problem?

Here's a Microsoft support article that may help you.
http://support.microsoft.com/kb/314477
Also - a Windows XP install on your Mac requires that you have an installer that includes at least Service Pack 2 (or SP2) on the same disk with the XP install. I think that error that you get may be the normal result when you try to install without SP2 or higher. Does your Windows installer CD show SP2 on the label of the CD?

I deleted the XP partition and created it form windows installation disc, that was the problem, now after I booted from Mac partition and run BootCamp, I created the windows partition from there, it is working perfectly till now,
I will disturb you later if I get more problems.
You R very helpful

Can I found drivers for XP on iMac A1224

The drivers are on the Mac OS X Install/Restore CD/DVD. Pop in your Mac OS X CD or DVD while booted in Windows and the driver install should automatically start.

I don't have the CD Mac OS or any restore disc
And I need to install the drivers, I did back up some drivers before reinstalling windows, and I did recover some of the drivers but still I need some

In Device Manager I still Have VGA, Bluetooth, PCI Device, as unidentified, anybody knows where I can find drivers for iMac A1224

I don't have the CD Mac OS

Why? Having a Mac without the install/restore CDs/DVDs is like having a car without keys: pretty darn useless!

Where are the CDs/DVDs that came with the computer when you purchased it? That is the best (and pretty much only) place to acquire the drivers needed.

The A1224 iMac was first sold before Leopard (10.5) was released. If this iMac shipped with 10.4 - then no boot camp drivers on that old restore disk anyway. Any Leopard (or Snow Leopard) installer disk will have those Windows drivers on the DVD.

Dear ElDiabloConCaCa,
in fact this Mac and like others we do have, was a donation from the USAID for the Community of Blinds " Y.A.B " for whom I am doing a Favour, and that is the reason we do not have the CDs/DVDs. If you may help us find the drivers so we may download, you'll be participating in helping this community.
Thank you & god bless you all

I have searched for XP drivers to download for iMac A1224, how can I get the restore CDs/DVD's ?

The XP drivers are provided by Boot Camp application.

The restore discs for the Mac... only place to get CPU specific ones if they are lost is AppleCare, but that is not a free option. Always, always keep securely the discs you get with a Mac so you will not run to this problem.
For an Intel based Mac, it will be cheaper to buy Mac OS X 10.6 discs than get replacement CPU specific ones.

Why not run Windows XP in Virtualbox?