I want to extend an exsisting hardwood floor(solid 3/4 oak) into
another room.  Some of the planks on the existing floor are very long
and I would not like to replace all of the planks.  Some are short and
can be replaced.  My questions are: What is the best process for
interleaving the old flooring with the new and, any tool suggestions
for performing the work.

If you want to extend your hardwood floor into another room
wood4floors have printable instructions for fitting wood floors their
address is
http://www.wood4floors.co.uk
In particular their Installing Hardwood Floors section has a list of
guides for fitting wooden flooring and details tools and types of
flooring profiles you may require.
 
regards