Backtrack 5 is ubuntu based OS that has many penetration tool installed inside. it usually used by people to begin learning about networking and hacking. u can download the source in http://www.backtrack-linux.org/downloads/ and choose which one meets your need. that page will ask u
1. VM Flavor / Desktop Environment : GNOME and KDE .
2. Architecture : Arm, 32bit, 64bit
3. Image : ISO/VMware
for example u’re planning to install it in your laptop, u can choose : KDE, 32bit, ISO , then click download. ISO image also provides ability to use Unetbotin. Using software Unetbootin, u can create bootable BT5 in Flashdisk/External Harddrive, it will help you who doesn’t want to install this OS directly on your Laptop. U can download Unetbootin in http://unetbootin.sourceforge.net/. Tutorial to create bootable drive also provided in that website.
U can install BT5 to your computer using the ISO images, u can burn ISO image to DVD, or simply use the flashdisk with bootable BT5 (Using Unetbootin).
1. Plug-in the bootable DVD/flash drive.
2. After some proccess Enter the default login name : root and the default password : toor
3. To load the desktop enter command: startx
4. Choose / click install.sh located in top-left corner of the screen
5. Follow the instruction
BT5 provides some options in installation proccess, u can choose guided option or advanced one. in guided option u are given options to choose whether u want to create dual boot OS or not, in advanced one, u will specify the partition by yourself. here i choose guided dual boot OS and then choose the part of the disk that will be taken for BT5 partition. For trial i just allocate 10 GB. Then, the installation continue and when it has finished, reboot your system and you will get BT5 as default booted OS.