The exhibitor list for the 2004 Tokyo Game Show has been released and Nintendo's name is currently lacking from it, according to Cube-Europe. It's unknown whether or not the list is final.
Nintendo has been known to make a small to no appearance at prior Tokyo Game Shows preferring to hold its own exclusive show called Space World. For the past couple years however Nintendo has opted not holding Space World to save money. Nintendo would traditionally hold the Space World show at the Makahuri Messe center, however Nintendo has not booked any space or dates, which likely means there will be no Space World this year, contrary to rumors.
It's still possible Nintendo will hold a smaller event later this year in preparation for the release of the Nintendo DS.