How to install Windows 8 on Ubuntu 12.04(ubuntu installed first)?

First off all , Here is not support for Windows. Is for UBUNTU.

Second , you said iso file. Don't say that. Everyone can understand that you referring in illegal copy. Except if you are Ms developer and took it from MSDN site :-P

Please close this question.

Thanks

The .iso may well be the release preview, which is totally legal, as for installing it, I presume that you burn it to a cd, and boot from the cd

Oh yes. I apologize for my suspiciousness. It is true that MS offers .iso images for preview. So I assume you have an .iso like this , you just burn it to a dvd and install windows 8 to an already located space , you created before with gparted.

summarized , here are the steps you must follow

1. Open gparted from Ubuntu and create a space for windows 8 . NTFS filesystem

2. Burn the .iso to a DVD and boot from there and install Windows 8 to the created NTFS space.

3. Boot from a LiveCD/Usb of Ubuntu and restore Grub-bootloader so you will be able to boot in any of your Operating Systems.
Here is the restore tutorial : https://help.ubuntu.com/community/Boot-Repair , follow the 2nd option , just two simple commands in terminal from a LiveCD/Usb.

Thanks and good luck.

You can resize the Ext4 and install Windows to the new free space. You will need to boot back to the Ubuntu CD as the Windows installer will blindly overwrite the MBR with it's own bootloader.

Obviously run a full backup in case of catastrophe

I don't have the Ubuntu USB from which I had installed earlier. So where can I get the bootloader?

You can make a new one. USB, CD or SD card is fine.

@actionparsnip
How do I make a new bootloader? Do I get the ubuntu iso file, make a bootable USB out of it and boot from it?
I am a really newbie and missing a lot of basics. Sorry if I am irritating.
Thanks for helping!

Thanks actionparsnip, that solved my question.