root@petita-laptop-l:/# apt-get update
Hit http://security.ubuntu.com jaunty-security Release.gpg               
Hit http://archive.ubuntu.com jaunty Release.gpg                         
Hit http://archive.ubuntu.com jaunty-updates Release.gpg
Hit http://security.ubuntu.com jaunty-security Release
Hit http://archive.ubuntu.com jaunty Release  
Hit http://security.ubuntu.com jaunty-security/main Packages        
Hit http://archive.ubuntu.com jaunty-updates Release
Hit http://security.ubuntu.com jaunty-security/restricted Packages
Hit http://security.ubuntu.com jaunty-security/universe Packages
Hit http://security.ubuntu.com jaunty-security/multiverse Packages
Hit http://archive.ubuntu.com jaunty/main Packages
Hit http://archive.ubuntu.com jaunty/restricted Packages
Hit http://archive.ubuntu.com jaunty/universe Packages
Hit http://archive.ubuntu.com jaunty/multiverse Packages
Hit http://archive.ubuntu.com jaunty-updates/main Packages
Hit http://archive.ubuntu.com jaunty-updates/restricted Packages
Hit http://archive.ubuntu.com jaunty-updates/universe Packages
Hit http://archive.ubuntu.com jaunty-updates/multiverse Packages
Reading package lists... Done
root@petita-laptop-l:/# apt-get install ubuntu-desktop
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.

Since you only requested a single operation it is extremely likely that
the package is simply not installable and a bug report against
that package should be filed.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
  ubuntu-desktop: Depends: pulseaudio but it is not going to be installed
E: Broken packages