Installing PostGIS 2.0

Dear all,

I'm currently running PostgresSQL 8.4 with PostGIS 1.5, but figured
it's about time that I upgraded to a more recent version. I had
decided not to do this until now as I wanted to use PgRouting, but I
see that Sanak has wonderfully made this possible now, so just now I
downloaded and installed PostgresSQL 9.1. This seemed to go well.
However I then launched Stack Builder and asked it to download and
install PostGIS 2.0. Towards the end of this process however I was
given an error which was :

_____
Database installation of PostGIS functions failed
_____


It asked me if I wanted to view the error text, so I did, and it said:

____
ERROR:  syntax error at or near "EXTENSION"
LINE 1: CREATE EXTENSION postgis;
               ^
____

Would someone be able to explain what is going on please? I 'finished'
the installation at this point and can actually see a PostGIS2.0
template in my PostgresSQL 9.1 installation, so actually all has gone
well?

Thanks

James