woody apt: dowloading from different releases

["Bruce Miller" <bruce.miller@ottawa.com>]

I am running Libranet 1.191 updated to woody with KDE from sid. 
The version of apt in woody has been 0.5.3; as of yesterday, it 
upgraded to 0.5.4.

This version of apt has a feature to download a file from a different 
release without changing /etc/apt/sources.list. N.B. The feature is 
new as of woody; it does not yet exist in the potato version of apt. 
The syntax is: ``apt-get install foobar/release" where release is one 
of stable|testing|unstable.

So far, it is not working. If I try to update an existing application, I 
get the error message: Release "unstable" for "foobar" was not 
found

If I try to install a new application from the different release, I get 
something to the effect that package "foobar" not found.

Is there something obvious which I am missing?