ootloader) is the bootloader used by many Linux distributions including Ubuntu and Linux Mint. "/boot/grub/menu.lst" is the file that generates the list of Operating Systems you see every time you boot your computer.
Each Linux Operating System installed on your computer installs a Grub bootloader, erasing and overwriting the Grub loader installed by any prior installation. When you installed Ubuntu, it installed a Grub loader that detected your Vista installation and set up the required dual boot system and menu (which you edited to make Vista the default operating system).
When Mint was installed it replaced Ubuntu's Grub with its own version, in the process setting up a multiboot menu with Mint as the default O.S. Each time another Linux distro is added, the same thing will happen (as long as the new distro uses Grub as its bootloader). The last O.S. installed will always be the default unless you edit the Grub menu for that
O.S. To regain Vista as your default O.S., you must edit the Grub menu in Mint just like you did in Ubuntu.
To avoid having to edit Grub from terminal, you can install a program called "startup manager". It is available from Synaptic Package Manager. Just open Synaptic and type "startupmanager" in the search box. There is a slight problem with the menu launcher for startup manager. See this for a fix: viewtopic.php?f=90&t=27518#p159803
. Startup manager will let you set your default O.S. without opening a terminal.
If Mint was installed after Ubuntu, its Grub will be the active bootloader so you should
be able to remove Ubuntu without impairing your ability to boot into Vista or Mint. I have never tried this so I am not certain, but it is the logical answer based on the way Grub works. I multi boot all the time (right now I have Vista plus four versions of Mint on my laptop) and what I normally do to remove an O.S. is install another O.S. over it. This automatically rewrites Grub to reflect the new setup.
Emorrp1 posted his reply while I was composing mine. I hope we don't confuse you with the two posts and between us we answer your questions. Emorrp1's suggestion to use a dedicated Boot partition is a good one if you will be doing much distro hopping or replacing O.S. with newer versions with any frequency. If some one had suggested it to me when I first began in Linux, I would have used it. Now I am so used to just re-editing Grub whenever required that I don't even think about a dedicated Grub installation.