Web page instructions for Squeeze say to use:

deb 
http://ppa.quickbuild.pearsoncomputing.net/trinity/trinity-v3.5.13/debian squeeze 
main

I put that (and the other 3 TDE lines) in 
/etc/apt/sources.list.d/trinity.list manually.

When "trinity-keyring" gets installed it actually writes to (and 
overwrites if already exists) that file with this entry:

# Trinity repositories

deb 
http://ppa.quickbuild.pearsoncomputing.net/trinity/trinity-v3.5.13/ubuntu squeeze 
main
deb-src 
http://ppa.quickbuild.pearsoncomputing.net/trinity/trinity-v3.5.13/ubuntu squeeze 
main
deb 
http://ppa.quickbuild.pearsoncomputing.net/trinity/trinity-builddeps-v3.5.13/ubuntu 
squeeze main
deb-src 
http://ppa.quickbuild.pearsoncomputing.net/trinity/trinity-builddeps-v3.5.13/ubuntu 
squeeze main

It will work like that but not till after another apt-get update (that 
played havoc with my custom install scripts) I had to strip the deb 
package down to find out what had altered my list.

  ?