RE: No "encapsulation" command on IOS 12.2(12a) ??

Kind of OT for NANOG, you should go to cisco-nsp for these kinds of
questions.

However, to answer your question anyway you need an IP plus version of IOS
to get 802.1q/ISL subifs on a 36xx router. That's only plain IP (c3620-i
vs. c3620-is)