You need to have SAS/ACCESS Interface to ODBC installed.
You need to install a PostgreSQL ODBC driver by downloading it from here:
Once you have a driver installed on your Windows machine (the same machine where SAS is located) you simply setup a DSN to where PostgreSQL is located:
Control Panel --> System and Security --> Administrative Tools --> Data Sources (ODBC)
Create a SYSTEM DSN, and select ADD
Select the PostgreSQL driver (ANSI) normally works well and then fill in the information.
Select the "TEST" button and if it works then you have a functioning DSN that you can use in SAS like this:
libname myconn odbc dsn=YourDSN user=PostgresUser password=PostPass schema=public;