You can use a live CD/DVD or a bootable flash drive or hard disk that has it installed. Once properly installed and configured, it will boot via the bootloader (GRUB in BIOS/CPM or EFI).
grub ana LILO are the two boot loader in Linux
Diskless Remote Boot in Linux was created on 2004-04-01.
/boot
If you have a USB drive and your BIOS supports booting from a USB device then try that.
No version of Linux is officially supported by Boot Camp. Assuming when you compile Linux From Scratch you include support for the Macintosh's hardware, it will work just fine when using Boot Camp to prepare the system.
Yes you can. Ubuntu's WUBI uses the Windows bootloader (NTLDR) to boot Linux. It also uses the Windows filesystem (NTFS). This, however, is not the traditional way to do things. The traditional way to dual-boot Linux and Windows is to use a generic bootloader such as Grub to boot both Windows and Linux.
No!
You can make it the default option in the bootloader. Or you could reinstall the Windows bootloader, but it will not allow you to boot Linux without modification.
As there are hundreds of Linux CDs, it is impossible to provide a comprehensive overview of what, if any, boot options they may provide.
Yes.
You can. But the Windows installation does not put an entry into it's boot menu, so you have to manually copy a boot sector, and modify the boot menu so you can boot Linux. Linux distributions expect that you may want to dual-boot, so they detect Windows and set up an option for it automatically. For convenience's sake, it is far easier to install Windows first.
So that you can choose to load either linux or (usually) windows.