I have Ubuntu 12.04 installed in a computer. There are no other Operating Systems in this. I need to uninstall ubuntu so that I have a clean empty Hard Disk. There is nothing I need to save there. How can I do this?

THANK you,I like Darik's Boot and Nuke - http://dban.org/
Go to the download page, burn the iso file to a blank CD and boot from it. Follow prompts to erase all data on the hard disk. It WILL erase everything, so make sure you're actually ready to do that.

If you plan to just install a new operating system right after erasing the drive, you can skip DBAN and just reformat the hard drive during the installation process.Quote from: TechnoGeek on April 07, 2013, 11:36:05 AM

I like Darik's Boot and Nuke - http://dban.org/
Go to the download page, burn the iso file to a blank CD and boot from it. Follow prompts to erase all data on the hard disk. It WILL erase everything, so make sure you're actually ready to do that.

If you plan to just install a new operating system right after erasing the drive, you can skip DBAN and just reformat the hard drive during the installation process.

(1) When DBAN erases all data, do I lose the disk space of the partition that contained the Opereating system although DBAN erases everything?

(2) I hope to install Windows XP Professional but I know nothing about partitioning. What should I do?

DBAN restores the drive to a completely blank and unpartitioned state of its full original size, like how it would be when it came out of the factory.
If you want to install Windows XP Professional and completely remove ubuntu, you don't actually have to use a tool like DBAN to erase the hard drive at all. During windows XP setup, instruct it to erase or delete the partition(s) that already exist and create a new partition to install XP to. This page on Microsoft's site has instructions on how to do this during setup (About halfway down the page, look for the heading "How to partition and format the hard disk by using the Windows XP Setup program")

During installation I am given the choice of two file systems - NTFS AND FAT. What are the pro's and con's of the two systems? Which do you think is the better choice?

Regards,

You can use either the NTFS or FAT file systems. NTFS is the preferred file system to format the hard disk unless you want to run an earlier version of Windows that cannot read NTFS partitions. For additional information about the differences between the FAT and NTFS file systems, click the following ARTICLE numbers...

From the same page I linked earlier:
Basically, use NTFS unless you know for some reason that you have to use FAT. You almost certainly don't unless you need to use Windows 95/98/ME or older.

DBAN restores the drive to a completely blank and unpartitioned state of its full original size, like how it would be when it came out of the factory.
If you want to install Windows XP Professional and completely remove ubuntu, you don't actually have to use a tool like DBAN to erase the hard drive at all. During windows XP setup, instruct it to erase or delete the partition(s) that already exist and create a new partition to install XP to. This page on Microsoft's site has instructions on how to do this during setup (About halfway down the page, look for the heading "How to partition and format the hard disk by using the Windows XP Setup program")