dual-boot 2 linux system

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Linux

I have 2 questions:

1. I saw an article in linuxbsdos about dual boot BackTrack after Ubuntu:
http://www.linuxbsdos.com/2012/03/23/how-to-dual-boot-backtrack-5-r2-and-ubuntu-12-04/
How to dual-boot BackTrack 5 R2 and Ubuntu 12.04

It only shrink the partition of the Ubuntu root partition, I am wondering why the BackTrack doesn't need the boot partition?

2. Dual boot Ubuntun and Win Xp:
I installed Ubuntun after xp, when I partition my disk, the next step is select Device for boot loader installation, I installed 2 times, first I select the /boot partition for my Ubuntu, but it doesn't show in the start menu, the next time I select the dev/sda, and this works, I want to know why? because I saw in some article it says you should select the boot loader with /boot partition. otherwise it will overrides your MBR.