HP has ported the 21.2 version of Emacs dated 2002-03-16 to it’s OSS personality of NSK and posted it to ITUG. To download this port click here and check the [editor] box and then click the [begin search] button at the bottom of the page.
If you are accessing the system with a terminal emulator from a desktop machine it seems a silly thing to run an old version of Emacs and compete with other system users by running the Emacs port. It makes more sense to run a much newer version of Emacs on your desktop machine and use TrampMode or AngeFtp to access files on the Tandem box.
See TandemNskSupport for info on major modes and utilities specific to the Tandem/HP Guardian/NSK environment.