Advice on running two database clusters on one server machine

Hi all,

We are implementing a hospital information system and a human 
resources/payroll processing system on two identical dedicated servers with 
two Xeon Quad Core processors and 32 GB RAM each, both servers being attached 
via FC to a SAN, and both applications running on PostgreSQL 8.3 / CentOS 51.

We are wondering about the advisability to distribute the databases between 
the two server machines, both machines acting as active production systems 
for one application each, and as warm standby servers for the other, using 
WAL shipping to a second database cluster running on another port on each of 
the two server machines.

What would be the performance cost of doing so, rather than running all 
databases on one database cluster on one machine, and using the second 
machine as a warm standby server for all databases of the two applications?

What other considerations should we take into account? We have no prior 
experience with PostgeSQL administration, having run our previous systems on 
Windows Servers and MS SQL Server.

Thanks to all for your input!

Andreas Philipp
Clínica Universitaria Teletón
Chía, Colombia