If you only disable Secure Boot, there is no problem in some cases. You are only disabling the part that creates the most problem between Windows and Linux, which is the one that prevents Ubuntu from booting correctly. In either case, I encourage you to first try to install Ubuntu with UEFI/Secureboot, since in most cases it will work. if you disable any of them and install Ubuntu, you might not be able to boot to Windows 8 afterwards through the GRUB Boot Menu.
Make sure you have already backed up anything on your old drive that you want and then go to Pendrivelinux.com and follow one of their step by step methods. I recommend Linix Mint as a good version to use.
The MD5 hash is really protection against hackers (because no one can change the file without changing the MD5). It should match although a great number of people don't bother checking it if they get it from the official site.
There are a couple of reasons it wouldn't match. I think the most likely is that WinMd5sum is wrong (or you might have made a mistake using it). You might want to try a different MD5sum tool.
I noticed you chose xfce, and 32-bit. I am curious how you made that decision (this has nothing to do with your MD5 issue).
Are you checking the md5 of the downloaded file or a burned DVD?
Check the MD5
You’ve read the release notes, you just can’t wait to play with the new features or try
Linux Mint, and your download just finished successfully. You’re ready to burn a DVD
and to boot on it… but hey! Wait for a second!
If that DVD is faulty you will experience weird bugs and will have a lot of trouble finding help. The two most common reasons for a DVD to be faulty are:
An issue with the download causing problems in your ISO file
An error during the burn process that alters the contents of your burned liveDVD
The MD5 signature, which is present on the download page, provides a quick way for you to make sure that your ISO file is exactly like it should be. So, let’s check the ISO file you just downloaded before we burn it and save ourselves from a lot of potential problems.
Once the Virtual Linux machine is running the interface is pretty small