In my laptop I currently have Windows 7 and Ubuntu 12.04 in dual-boot.
I tried the newest version of WattOS (based in Ubuntu) today from a live-USB, and decided to install it to my hard drive, to use whenever I am completely dependent on battery energy.
However I don't want to create any conflicts and boot problems, specially because my DVD drive is not working and thus I am unable to use Windows 7 DVD to repair MBR.
What is the safest way to install a second Linux distribution (in this case Watt OS) and update Grub Menu, without major trouble?
There's no difference between dual-booting and triple- (or quadruple- etc.) booting, at least when the OS being installed is Linux - you just prepare an empty partition and install your OS there.
Supposedly, the GRUB will be re-installed so its second stage will be on the partition of the last installed OS, but it should find all other OSes and add them to the menu just the same.
I'm not sure how repairing MBR with Windows DVD relates here though - you aren't using Windows bootloader as your primary bootloader, are you?
I have already installed Windows 7,Ubuntu 12.04 and Fedora 17 (triple boot)
The easy way to do this:
Make sure it will not go beyond the 4 primary partitions if it so then your PC will not boot up
You can make extra partition by GParted tool but it will not more than 4 in case of primary partition while other extended partition is allowed
After having the sufficient space for third Linux distribution, install it .
Then, I re-install grub2 of Ubuntu
Here is the video http://www.youtube.com/watch?v=8lod8sRb_6I
Now you are able to use all the three OS installed in your PC
If the other distribution is not shown in grub2 menu then you can update Ubuntu grub2. See http://www.youtube.com/watch?v=WJDcyAncmRY