The guide looked okay, from the quick glance of it I did. There's not really much I can clarify with that.
Now, as for what you're asking from what you quoted here: the other part you're seeing is that you will need to replace the file in either C:\Windows\system32 or C:\Windows\SysWOW64 to complete the change. But there's a problem with that. Windows is usually installed by default on C:, but may not always be C:, and also, Gnu/Linux is a *nix-like system that identifies hard disks by /dev/sda, /dev/hda, etc. and their partitions are listed by number. So, for instance, /dev/sda3 may be the Windows partition on a modern EFI disk, where the System and EFI partitions come first. This is important because Ubuntu is a Gnu/Linux distribution.
And also, you will need to download Ubuntu. You can do that from ubuntu.com, and find the Download page. From there, download either a 32-bit or 64-bit ISO. Now, if you bought an AMD or Intel-based Windows 8 PC, you most likely have a 64-bit computer (in this case, you will need the amd64 version, because you probably also need the Secure Boot support only in the amd64 ISO). Once you have this ISO, attach a DVD burner, find a blank DVD writable, then right-click your downloaded Ubuntu ISO. From here, click "Burn to disc..." then Burn again. Reboot your computer using your new Ubuntu DVD.
Now, finally, if I may say one last thing, supposing that you follow the instructions in the article for editing your system file properly, and mine here for Ubuntu, then please back up your original copy. Even the article you linked to mentions to do this "at your own risk" and I would say the same thing.
So... in conclusion, be CAREFUL. If you want a cool sound to play over the embedded system startup sound, I would just uncheck the startup sound option in the sounds control panel, then just put a batch script in your Startup folder that plays your file, but it's not a very wise idea to mess with a system file unless you have to.
Good luck.