install ubuntu from a running Linux system

[Mihamina Rakotomandimby (R12y)]

Hi,
What is the procedure, nowadays, to install a 64 bit Ubuntu from a 
running system?
It's a dedicated server, which can boot a "rescue" system.
The hosting solution provides only 32 bit OSes and I want to install a
64 bit one (no matter it's worth or not, it's just a wish).

 From the "rescue" mode of the server, I can chroot to the main hard drive.

Searching with "install ubuntu from live system" only gives me how to 
install from a Live CD.

Thanks for ny tips.

-- 
Chef de projet chez Vectoris
http://www.google.com/search?q=mihamina+rakotomandimby
System: xUbuntu 8.10 with almost all from package install