Problems with `nnweb' mode (was: Old messages missing on the present newsgroup)

[Rodolfo Medina]

In Gnus Manual there is:

-----------------------------------------------------------------------
The `nnweb' back end allows an easy interface to the mighty search
engine.  You create an `nnweb' group, enter a search pattern, and then
enter the group and read the articles like you would any normal group.
The `G w' command in the group buffer (*note Foreign Groups::) will do
this in an easy-to-use fashion.

[...]

   You must have the `url' and `W3' package or those alternatives (try
`customize-group' on the `mm-url' variable group) installed to be able
to use `nnweb'.
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I installed emacs-w3m and also the `url' package,
but the message gnus finds with the above procedure (`G w' etcetera)
are all completely blank.

Any help?
Thanks,
Rodolfo