I have read this question: Install PostGIS v2 for PostgreSQL v9.2, but it didn't resolve my problem.
I added the PostgreSQL backports PPA and installed the
postgresql-9.2 package, but there is no package for PostGIS.
How to Get Started with PostGIS 2.0 on Ubuntu 12.04 (precise)
(only tested on a Oracle VM) see Migrating to Linux from Windows previous install.
http://trac.osgeo.org/postgis/wiki/UsersWikiPostGIS20Ubuntu1204 (replace postgresql-9.1 with postgresql-9.2)