I have a problem with a Backtrack 5 installation. So I just want to install Backtrack 5 tool on my Ubuntu 11.10. Can it run on ubuntu 11.10?
You don't install BackTrack on another OS.
You either run it as a LiveCD, or you install it on a disk as the operating system. I assume you want to keep your existing operating system (your Ubuntu install) so don't try and install BackTrack over it; run it as a LiveCD or install it on another disk or partition.
Backtrack on USB stick works perfectly for penetration testing. I have one USB stick just for this purpose. You will need to ensure your machine can boot from USB (set this in the BIOS) and that the install you have on the stick is a Live install (ie bootable) and it should boot to BackTrack without any problem.
Update: the BackTrack FAQ says this about using BackTrack tools in Ubuntu and vice versa:
Why cant I just add the Backtrack repositories to my Ubuntu install or the Ubuntu repositories to my Backtrack install ?
We highly recommend against this action because Backtrack tools are built with many custom features, libraries and kernel. We have no way of knowing how they will perform on a non Backtrack distribution, plus you will very quickly break your install. Also if you chose to add the ubuntu repositories to your Backtrack install, you will most certainly break your entire Backtrack install very quickly. We do a lot of testing to ensure that all packages in our repo will work together without causing problems. If you decide on this course of action you do so entirely at your own risk and the backtrack team will not offer any support in any way.