How does one delete or remove Windows XP from the Hard Drive while using Ubuntu and not re-installing Ubuntu again?
I am assuming you have both Ubuntu and WindowsXP installed in a "permanent", dual-boot install, not a Wubi install. Also I'm assuming that your computer loads into Ubuntu by default. If not, please don't do this just yet. Change Ubuntu to your default first, then delete Windows.
Search for the "Disk Utility" program and open it. Have a look around at the disks on your left, and you should find the disk (or 'partition' if you have windows installed on the same disk as linux) that Windows XP is on.
Under "Volumes" select the Windows partition
And then click "Format Volume". This will wipe out the XP installation, and you can choose to give the drive another name for use in Linux. (By the way, leave "Type" set to "Ext4").
If the Windows partition was on the same drive as your Linux, depending on how it's setup you might also be able to choose "Delete Partition" and then resize your Linux to fill up the space, but this doesn't always work. Easier to format it and give it a new name.