how to install virtual box on backtrack without error

Make friends who menggalami errors when installing Virtual Box on Backtrack 5, then try the following manner, ^ ^

1. Download Virtual Box here
2. Then Perform installation as below:

root @ bt: ~ / Downloads # ./VirtualBox-4.0.10-72479-Linux_x86.run
bash: ./VirtualBox-4.0.10-72479-Linux_x86.run: Permission denied
root @ bt: ~ / Downloads # chmod + x VirtualBox-4.0.10-72 479-Linux_x86.run
root @ bt: ~ / Downloads # ./VirtualBox-4.0.10-72479-Linux_x86.run
Verifying archive integrity ... All good.
Uncompressing VirtualBox for Linux installation ...........
VirtualBox Version 4.0.10 r72479 (2011-06-24T13: 43:27 Z) installer
Installing VirtualBox to / opt / VirtualBox
tar: Record size = 8 blocks
Python found: python bindings installing ...
Building the VirtualBox kernel modules

VirtualBox has been installed successfully.

Will you find useful information about using VirtualBox in the user manual
   / opt / VirtualBox / UserManual.pdf
and in the user FAQ
   http://www.virtualbox.org/wiki/User_FAQ

We Hope that you enjoy using VirtualBox.

good luck...