Mac Pro install disk keeps ejecting itself
According to everymac.com, your Mac is a 2006 model which was discontinued January 8, 2008. (I made the assumption 2.66QX means 2.66 GHz Quad Core Xeon) This model originally was designed to run OS X 10.4.7. Since the 
Mac OS X v10.6.2 Update is dated Nov 9, 2009, I doubt the disc you have is the correct one for this model Mac.

The OS X 10.7.5 (Lion) was the last version designed for your Mac model. 


  Note: Since this model has a 32 bit EFI, you can only run 32 bit EFI booting operation systems. However, you may be able to run 64 bit BIOS booting operating systems such as Windows and some versions of Linux.


If you were to purchase Lion from Apple, then a requirement to install would be to have Snow Leopard already installed. In other words, the DMG file only offers an upgrade to Lion. You probably can not use the DMG file to create a bootable installer. You can read the requirements from the Apple Lion website given in the above link.

You would not need a Apple ID to install Snow Leopard, but the installer will still ask. You can decline to give an Apple ID if you wish. Snow Leopard was released on a DL DVD. Apple still sells Snow Leopard DVDs, but you can also download an ISO from the internet. Instructions are given below for creating a Snow Leopard USB flash drive installer. If you chose to burn a DVD, then you will need a DL DVD, since the contents of the ISO is over 4.7 GB.

Once you have Snow Leopard installed, you should install all the available Snow Leopard updates. This would update Snow Leopard to OS X 10.6.8. From here, you could upgrade to Lion by using a purchased DMG file.

Creating a USB Flash Drive Installer from a Snow Leopard ISO File.

This was done use an iMac (21.5-inch, Mid 2011) 2.5 GHz Intel Core i5 with MacOS High Sierra 10.13.6 installed. The flash drive was testing using VirtualBox Version Version 5.2.26 r128414 (Qt5.6.3). The flash drive needs to be at least 8 GB in size.


Use the Finder application to mount the Snow Leopard ISO file.
Use the Disk Utility application to erase the flash drive, as shown below. I chose the default name Untitled. Finally, click on the Erase button.


Highlight the name Untitled, then click on the Restore button on the top of the Disk Utility application window. In the popup window, select restore from Mac OS X Install DVD, as shown below. Finally, click on the Restore button in the popup window.


The flash drive was tested using Virtual Box. Other than selecting the flash drive, I used the default settings for a 64 bit Snow Leopard installation. After booting from the flash drive, you need to use the Disk Utility application to erase the internal drive before installing Snow Leopard. Basically, select the setting shown below, then click on the Erase... button.


The result is shown below. Make sure the partition map scheme is GUID Partition Table.


Return to the Mac OS Installer and choose to install to the Macintosh HD disk.


When the installer finishes you should get a Welcome window similar to what is shown below.



The result after answering all the questions is shown below. I selected About This Mac from the menu bar.


Software update includes OS X 10.6.8.