The link_node module allows users to link to another node from the body of another node.
The syntax of these links ("[node:NNNN]") is incompatible with the attached_node module, which embeds the body of nodes rather than a link to them.
Once installed (see README in the attached archive) you (or any user who can post) can add an embedded link to any page using the syntax:
[node:NNN]
The tag format is fairly simple. The most basic tag would be in the following form:
[node:<node id>]Parameters follow the <node id> part and are comma separated name="value" pairs:
[node:<node id>,title="Original version of the picture"]
Note that the values must be encased in double quotes. This is to allow users to include commas in the value. The side effect is that double quotes cannot be used (currently) without causing problems.
The main project page is over on the Drupal site itself: http://drupal.org/project/link_node