How can I install Windows XP after Ubuntu 9.04 was installed ??

The linux system does not have to read the XP cd. The XP cd is bootable and will allow you to install windows from it. You do NOT boot to linux then run the XP CD.

If you want to install Windows you will need some unpartitioned space. If you have not left unpartitioned space (which you shoud have if a dual boot was your intention from the start) then you will need to boot to the live CD desktop to resize the current partitions. The XP CD does not have this functionality. If you have left unallocated space, miss the next paragraph.

Before you undertake this I strongly suggest you make sure your ackups are recent as the resizing may result in data loss (Linux comes with zero SLA and zero garuntees) You can resize the ext3/ext2/whatever partitions to make some unallocated space. This will then be usable by the windows installer

The windows installer is not very intelligent at all and WILL overwrite whatever is in the boot sector with NTLDR. You will then not have grub after the install of windows. To get it back you will need to boot to the live cd and reinstall grub. You may then have to add an option for the XP boot but this is very easy.

Hi :)

You don't have to install Windows as Ubuntu almost absolutely everything that Windows can and a lot more in most cases
https://help.ubuntu.com/community/SwitchingToUbuntu/FromWindows
https://help.ubuntu.com/community/Antivirushttps://help.ubuntu.com/community/Antivirus

If you really must use Windows programs after looking around for a native linux equivalent then they almost always run in Wine (Wine Is Not an Emulator)
http://appdb.winehq.org/

But if that's not enough then it might be worth learning ow to set up a Virtual Machine inside Ubuntu, perhaps using VirtualBox and then install Windows inside that
https://help.ubuntu.com/community/VirtualMachines
https://help.ubuntu.com/community/VirtualBox
This (and Wine) has the advantage that programs are effectively running inside Ubuntu and it may be possible to copy&paste between programs this way.

Alternatively you might want to try for a full proper install of Windows as part of a dual-boot.
https://help.ubuntu.com/community/WindowsDualBoot

Ok, so why did i start from the other way around? Windows is really quite tough to install and well worth avoiding if possible. Usually machines are bought with Windows pre-installed so a lot of the fuss is dealt with by experts well used to the particular machine and the usual Windows problems, as you'll find out. After installing Windows you'll then need to register it or use some pirated software to make it seem like a legit version and at least one crack has a virus really well built into it. Then you'll need to install a lot of the type of programs that will have already been installed in Ubuntu (or most other linux versions). These ar usually quite expensive but luckily some of the linux ones have been ported over to Windows so it might be worth installing the Windows versions of
http://download.openoffice.org/
http://www.mozillamessaging.com/en-US/thunderbird/
http://www.gimp.org/windows/
and of course Windows will demand that you install a lot of updates, but don't worry it'll tell you when and it'll reboot your machine for you at various points during the update process rather than asking for permission and making sure you're not busy with something at the time. As you can tell i find Windows really irritating to install and avoid it whenever possible. Ubuntu does everything i need and a whole lot more :)

Good luck and regards from
Tom :)

You might want to try booting up the machine from the Xp cd. Simply put the Xp cd in the cd/dvd-drive and shutdown your machine. When you switch your machine on again it should 'boot into the cd'. This guide might help although it's written for Ubuntu rather than Xp.
https://help.ubuntu.com/community/BootFromCD
Note that as ActionParsnip says you will need to create some unpartitioned space on your drive, or at least a partition formatted to ntfs/fat32. I would use "gparted" to help create that space for Xp
https://help.ubuntu.com/community/HowtoPartition

Windows tends to have a nasty habit of wiping out anything else on your drive when you try to install it so take care! This guide might help
https://help.ubuntu.com/community/WindowsDualBoot

Assuming everything goes well then Windows will have only "fixed" your mbr making it impossible to boot into Ubuntu. At this point this guide might help
https://help.ubuntu.com/community/WindowsDualBoot#Recovering%20GRUB%20after%20reinstalling%20Windows

Good luck and regards from
Tom :)

This might helps you http://davestechsupport.com/blog/2008/03/22/how-to-install-windows-after-ubuntu-with-gparted/

Hope this helps

@ Ken Appell
What information are you missing?

Hi :)

Have you been able to try the new Ubuntu 10.04 before it gets officially released?
http://www.ubuntulinux.org/testing/lucid/beta2
Trying it as a LiveCd or as an extra dual/multi-boot would be ideal. Developers and everyone are keen to try to iron out any problems before 10.04 gets officially released so you might find faster & more effective answers to your bug reports which would make 10.04 work better on your system for you

Thanks and regards from
Tom :)