Normally, this is the default behavior when you install most Linux distros and it finds another OS available, whether Windows or Linux. The methods should be the same, except that for windows, you need to make sure you install windows first.
The second Linux distro to be installed will usually detect the existing one, and create a Grub menu for both.
However, the second one will assume it is the main OS, and will setup Grub to look for the configuration file in its own partition, in
One problem here may be that BackTrack appears to be based on Ubuntu, and perhaps you accidentally performed an upgrade rather than a new install. You should create a new partition, and make sure you install it alongside the existing OS. I usually create the partition first in gparted (actually, I already have some spare partitions for experimenting), then choose "Something Else" from the install menu.
I have a 1 TB drive, plus a second 500 GB drive, so disk space is not at a premium for me. I back up to the alternate drive, and also have an old Windows XP on it.
My main drive is partitioned as a single extended partition, no primary partitions at all. I created 3 or 4 20 GB partitions for my main and alternate Linux installs, some swap space, a bit of unused space for various things I've tried (such as /boot partition, /var, etc), and the rest - at the end of the partition - is a "shared" partition with audio, video, photos, documents, etc. I create symbolic links to this in various distros I use so I always have access to my personal stuff. I keep the home directory with the distro, and it has a lot of distro-dependent settings.
I mount the "shared" partition in any installation that needs it, using
/etc/fstab to mount the partition into
/mnt/shared. The shared partition contains directories such as "Documents", "Music", "Pictures", etc, and I create links to these directories in my home directory. The easy way to do this is to use Nautilus, highlight a directory, right-click and choose "Make a Link". For example, I do this for
/mnt/shared/documents, and Nautilus creates a link named "Link to documents". I cut and paste this link into my home directory, and if there are any files int
~/Documents, I move them to
/mnt/shared/documents. I then delete Documents in my home directory, and rename "Link to documents" to "Documents". If this is done without logging out, the link will inherit the special icon and will act just like the original.
Repeat this procedure for any other directories, like music, pictures, etc.
When I want to try out a version upgrade, I can copy my current version to a partition so I can go back to it, then I can upgrade without worry, and I always have my data available. It's very easy to copy anything I need from my home directory on a different distro, such as .bashrc, etc.
The only thing to be aware of is the grub configuration. I've accidentally deleted a partition that has the grub files, and this makes the system temporarily unbootable unless you know the drill to boot from the grub prompt - not really hard, but I usually need a guide to remember. But the best thing is to have a bootable rescue CD, such as the Super Grub Disk, which can fix these problems easily.