Minimum hardware requirements for Postgresql db

Dear all

We would be recommending to our ct. on the use of Postgresql db as compared
to MS SQL Server. We are targetting to use Redhat Linux ES v2.1, Postgresql
v7.3.4 and Postgresql ODBC 07.03.0100.

We would like to know the minimum specs required for our below target. The
minimum specs is referring to no. of CPU, memory, harddisk capacity, RAID
technology etc. And also the Postgresql parameters and configuration to run
such a system.

1) We will be running 2 x Postgresql db in the machine.

2) Total number of connections to be around 100. The connections from the
clients machines will be in ODBC and socket connections.

3) Estimated number of transactions to be written into the Postgresql db is
around 15000 records per day.

The growth rate in terms of number of connections is around 10% per year
and the data retention is kept on average at least for 18 months for the 2
databases.

Are there any reference books or sites that I can tap on for the above
requirement?

Thank you,
REgards.