Is replication from SQL Server 2008 to PostgreSql possible?
Only ORACLE and IBM-DB2 are officially supported as subscribers. Refer here and here for more details.

Also, from sql server 2012, this is being depreciated as well.

Heterogeneous replication to non-SQL Server subscribers is deprecated. Oracle Publishing is deprecated. To move data, create solutions using change data capture and SSIS.
 Caution :
This feature will be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.

Below is a blog post that I found that might be useful to you:  Replicating from MS SQL Server to PostgreSQL