Hi Daniele,
you may have the following in your /etc/apt/sources.list:

deb http://de.archive.ubuntu.com/ubuntu/ lucid main restricted
deb-src http://de.archive.ubuntu.com/ubuntu/ lucid main restricted
deb http://de.archive.ubuntu.com/ubuntu/ lucid-updates main restricted
deb-src http://de.archive.ubuntu.com/ubuntu/ lucid-updates main restricted
deb http://de.archive.ubuntu.com/ubuntu/ lucid universe
deb-src http://de.archive.ubuntu.com/ubuntu/ lucid universe
deb http://de.archive.ubuntu.com/ubuntu/ lucid-updates universe
deb-src http://de.archive.ubuntu.com/ubuntu/ lucid-updates universe
deb http://de.archive.ubuntu.com/ubuntu/ lucid multiverse
deb-src http://de.archive.ubuntu.com/ubuntu/ lucid multiverse
deb http://de.archive.ubuntu.com/ubuntu/ lucid-updates multiverse
deb-src http://de.archive.ubuntu.com/ubuntu/ lucid-updates multiverse
deb http://security.ubuntu.com/ubuntu lucid-security main restricted
deb-src http://security.ubuntu.com/ubuntu lucid-security main restricted
deb http://security.ubuntu.com/ubuntu lucid-security universe
deb-src http://security.ubuntu.com/ubuntu lucid-security universe
deb http://security.ubuntu.com/ubuntu lucid-security multiverse
deb-src http://security.ubuntu.com/ubuntu lucid-security multiverse
# Trinity
deb http://ppa.quickbuild.pearsoncomputing.net/trinity/trinity/debian squeeze 
main
deb-src http://ppa.quickbuild.pearsoncomputing.net/trinity/trinity/debian 
squeeze main
deb 
http://ppa.quickbuild.pearsoncomputing.net/trinity/trinity-builddeps/debian 
squeeze main
deb-src 
http://ppa.quickbuild.pearsoncomputing.net/trinity/trinity-builddeps/debian 
squeeze main

where lucid has to be replaced by maverick. I don't know if you need them all.
After editing /etc/apt/sources.list you have to run "sudo apt-get update".
-- 
Viele Gr��e,
Hartmut 

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