If you are using ArcGIS 10, then you can directly connect to the PostGIS Data using a Query layer, there is more information on this available here

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00s500000032000000.htm

** good to note this page does not view correctly in Chrome, so I have used IE to read

If you are using ArcGIS 10.0 or later, then you can directly connect to the PostGIS Data using a Query Layer, there is more information on this available in the help of each version:

• 10.4

To use the PostGIS geometry type, the database administrator must install PostGIS on the PostgreSQL database cluster. PostGIS is a third-party, open source installation. Once installed, the database administrator can use the PostGIS template database to create a database containing the PostGIS geometry type, or configure an existing database to use the PostGIS geometry type.

• 10.0 (this page may not view correctly in Chrome, so I have used IE to read)