Did you check the form? I answer a question similar to this earlier. The subject topic was "Saving Attachments to the local drive".
The concept is the same except you are going to attach it to another notes document.
My example shows how to get the attachment (embeddedObject).
Here is the URL:
http://www-10.lotus.com/ldd/nd6forum.nsf/55c38d716d632d9b8525689b005ba1c0/8783bcfe0021f32985256d6c003e1d3b?OpenDocument
HTH -- Cheers