He may be talking about a wire harness adapter. Our cars are a bit strange in the way that the antenna must carry power, b/c I get no power to my HU without the antenna plugged in, but plug the antenna in and it all works. Last Monday I installed a HU into my '93, and it was a really simple task. As far as mounting the HU everything was fine - I just used the stock mounting brackets from the old deck. I did, however, need to purchase an antenna adapter and a wire harness in order to properly install the HU.
If you do not have the factory mounting brackets, you can save youself some $$$ by finding literally any B13 Sentra/200SX and get the mounting brackets from there. Removal and installation is a snap, however there is one caviat - the roller on the center vents. It doesn't do much to begin with, but it needs to be disconnected before you can remove the center piece on the dash. That little cable is a pain to re-install as well, chances are you will not hook it up properly on the first few tries, but it's not that big of a deal. Anyways, for proper removal of the dash, view this link:
http://www.carstereohelp.com/stereoremovalNisSentra1.htm
