[CentOS] centos 5.2 install: mbr or no bootloader ?

I recently used a purchased  centos 5.2 dvd to install.
It all went smoothly, and I am up and running
automagically it seems to have upgraded itself to 5.3 Final

One peculiarity:
I believe I was given the choice of:
--installing the bootloader into mbr
or
--no bootloader install

I did not want my mbr overwritten, so  I chose  no bootloader

Why is there no choice of 1st sector of root partition?

or did I just miss it?


I wanted to chainload the centos install,
but that requires grub installed into 1st sector of root partition.
So after the os install
I used  knoppix livecd to
 > grub
  root (hd1,4)              # sdb5 is my centos partition
  setup (hd1,4)

and centos now loads from a chainloader +1    in my grub partition
So I have fixed it;
but curious as to why the install dvd didn't give me the choice there.

Jack