You don't need a separate boot loader, Ubuntu will use its own boot loader called GRUB that will give you the option between the Ubuntu install and your XP install.
You don't have to edit the MBR yourself, Ubuntu seriously does all of the foot work for you.
When I said install from windows, i meant you will install ubuntu on the same drive / partition as windows. When you do that with the .ISO CD that you booted from you will get a GUI and the option to install. Ubuntu will recognize the drive is in use and will ask you how much space you want to allocate to each OS install.
That is about the only reason I can think of to keep music files on a separate partition, so that if you need to reinstall the OS you don't have to backup your personal files / folders.