Backup Database

I have two Postgres databases (7.4 and 8.24) within the same network on 
LINUX platforms. Data sources go to both databases.

I'd like to set up one as a near real-time backup to the operational 
database.  Is it possible to incorporate a trigger upon update (or 
insert) on the operational 8.24 database to initiate an update (or 
insert) on the backup 7.4 database? 

How do most people set up a near real-time backup database?  Perhaps 
there is something else that acts like a trigger.  Any suggestions would 
be helpful.

Thanks.  Joanne