How to install Windows 10 partition on macOS X Server 10.6.8 without bootcamp?
Installing Windows without using the Bootcamp app is risky. However, I will guide you through the correct steps to accomplish this.

Please Note: This method is not encouraged by Apple and may lead to your Windows OS to fail, resulting in a major loss of data. Please perform these actions at your own risk. Only do the following if you are the administrator and owner of your Mac. Be sure to back up your Mac to prevent any major damage.

Back up your Mac with Time Machine - https://support.apple.com/en-us/HT201250

Let's start off by opening disk utility. Select the Hard Disk of your choice, and select the "Partition" Tab. Once on the tab, select the "+" button, a pop-up screen will appear. If you are using a more recent version of macOS, you will have an option to choose the size of your partition. Please be sure to choose a minimum of 30GB for your partition size, as this will be the boot of your new Windows Partition. If you are using an old version of MacOS X, you might not have the ability to choose the size of your partition.

Name your to partition whatever you want, I named mine Win10. Make sure to choose the "MS-Dos (Fat)" or "ExFat" option for your format. Once the partition has been created, you now want to boot into Windows 10. This part may be more complicated. To boot into Windows 10, you need a Bootable Media Device. This device could be a USB or DVD. Please follow the steps below to find out how to create a bootable media device for Windows 10.

USB Device: (Use another device to do this) (Recommended for newer Macs)

Before you begin: Make sure you have a USB Drive with at least 8GB of storage. When following the steps below, your device will be formatted. Please be sure to back up any files on the USB. Make sure you have a reliable Network Connection before downloading the ISO.

Download the Windows 10 Installation Media Tool from the link provided.

https://www.microsoft.com/en-us/software-download/windows10

Download, Install and Run the tool. Agree to the Terms and Conditions. You will be taken to a page where the tool will ask you what you want to do. Select "Create installation media for another PC". Select "Next". On the next page, choose your language. For the remaining boxes, be sure to select "Windows 10" for Edition and "64-bit (x64)" for Architecture. Select "Next". On the next page, select "USB flash drive". Select your drive and begin the installation. This download may take a few hours depending on your bandwidth and internet speed.

Once the download is complete, follow the remaining steps to finish off creating your bootable USB.

DVD: (You may use the same device to complete this) (Recommended for older Macs) (Must have internal or external DVD reader)

Before you begin: Make sure your DVD has at least 4.5GB of storage. When following the steps below, your device will be formatted. Please be sure to back up any files on the DVD. Make sure you have a reliable Network Connection before downloading the ISO.

Download the Windows 10 Installation Media Tool from the link provided.

https://www.microsoft.com/en-us/software-download/windows10

Download, Install and Run the tool. Agree to the Terms and Conditions. You will be taken to a page where the tool will ask you what you want to do. Select "Create installation media for another PC". Select "Next". On the next page, choose your language. For the remaining box, be sure to select "Windows 10" for Edition and "64-bit (x64)" for Architectue. Select "Next". On the next page, select "ISO file". Select your file location of choice where to download the ISO file. Keep in mind, the ISO file is very large. (About 4.5GB) Please make sure to choose a file with enough storage. Begin installation. This download may take a few hours depending on your bandwidth and internet speed.

Once the ISO file has been downloaded, burn it to a DVD. Please make sure your DVD is in the tray at all times during burning the ISO file. For more information on how to burn a file to a DVD, please see the link provided.

https://www.seagate.com/us/en/support/kb/how-to-burn-an-iso-image-onto-a-cddvd-rom-201431en/

Using the bootable media:

Once you have successfully made your bootable device, follow the steps to add the Windows 10 partition to your Mac Pro Server.

For USB: When starting up the Mac, hold down the "Option" key down while on the white screen. When several options appear on the screen, let go of the option key. Use the arrows to navigate to your USB name and select the Return key. You should soon appear on the screen to install Windows 10.

For DVD: (Make sure your DVD is in the DVD tray for your Mac!) When starting up the Mac, hold down the "C" key while on the white screen. This will automatically boot your Mac from the DVD. After a while, you will be taken to a screen to install Windows 10.

I hope this helped you! :)

Cheers, John Williams