I think you need to load the postgis extension to your database like

<pre>
CREATE EXTENSION postgis
</pre>

or load these files to your query window and run them in database 
<pre>
windows default: 
\Program files\Postgresql\8.4\share\contrib\postgis-2.0

postgis.sql
rtpostgis.sql
spatial_ref_sys.sql
topology.sql (if you want topology support)
</pre>