I recently purchased an XP upgrade and intended to install over the existing
XP system. Instead of that happening - a partition was created and now I have two XP systems running. How can I successfully remove one or the other as well as the partition that was created?

Try booting into the XP you want to keep and see if you can delete the other partition.

You can try this using Disk Management: Start/Run/ diskmgmt.msc
Right click in the partition area and see if the delete option is there.

If you cannot do this I would suggest a Clean Install of XP. I assume that you are trying to upgrade Pro over Home?

With an upgrade CD you will need proof of your preceding Windows. In other words using an XP Pro CD you will need to insert (when asked) a previous Windows CD to verify that you qualify for an upgrade.

If your Home was an OEM (pre-installed on computer) then you will be limited to an Upgrade (Repair) install unless you have a previous Windows OS CD e.g. 98.

This is a good guide to a Clean Install:

http://michaelstevenstech.com/cleanxpinstall.html#steps

Note 10b: If the hard drive or partition has a previous installation of XP you want to remove, choose to delete the partition by pressing "D". You will then be prompted to create a new partition in the empty space. This will remove all data from the deleted space.