Can someone explain this to a computer illiterate person? If I want to buy a second copy from Amazon, what do I need to do to keep the accounts seperate on one pc?
You can change the warband key that's activated in your computer's registry.
EDIT: Since someone already said this I'll explain how in detailed steps.
1/ Press the Windows key+R, opening Run, type 'regedit' in the field.
2/ Navigate to HKEY_CURRENT_USER\Software\MountAndBladeWarbandKeys.
3/ Double click serial_key.
4/ Paste in the key you want to use, you can save your keys in a notepad file or whatever.