What are you trying to do? If you have a copy of NAS 2.1,
you should already have the docs, right?
Or are you trying to migrate an old 2.1 application, and are trying to find a way to port the API's? (You can't just copy the JAR files, since they hook deep into the internals of the appserver.)
Anyway, the old NAS 2.1 (aka Kiva) API has remained largely unchanged. You can look here :
Kiva API, in the iAS docs if you need an API reference. I just wouldn't recommend spending a lot of time with these API's since they are completely deprecated.
David