High Availability Setup

I am currently using PostgreSQL v.7.0.2 and Enhydra for a project that will
ultimately require 25M transactions per day.  This will be hosted on a Sun
420R server maxed out with CPU's running off of Sun's high end storage
cluster.  My question is whether anyone has installed PostgreSQL in a
solution requiring this much scalability and if so, what sort of set up have
you used to handle this much load?  The environment does not require
absolute uptime.  The company that will be implementing this currently has
downtime of roughly 48 hours per year.  They currently run MySQL to perform
50K transactions per day on a single box running Linux.  I chose PostgreSQL
because there will be large queries running intermittently with many
INSERT's and smaller queries and I was concerned with the locking
functionality of MySQL.  Any comments as to anyone's experience on this
would greatly appreciated.

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Nathan Barnett