I am logged on to Windows using a Windows Live ID (@live.co.uk) what would the username and password be in this case?
I assume you want to access a share on your windows machine? In that case you would need to create a local user/password to be able to access the share from OSMC.
You can use your Windows Live ID password no problem. For the username check your C:\Users folder and one of the folder will be your username (if more than one person using your Windows 10 desktop).
Then in fstab use that username (not your Live ID email address) and the password (the same you are using to login to your desktop).
Works fine for me.