PostgreSQL scalability concerns

Hi,

  We are currently planning the deployment of our next generation enterprise database and we are wondering whether or
notPostgreSQL could do the heavy lifting that would be required.  My post is a little bit long but I hope it will
provideyou with information to allow someone to provide a definitive answer. 

  First, a little history about our current setup.  We are currently running SQL Server 2000 on Windows 2000 Advanced
Serveron HA clustered Dell boxes with 4 cpu's and 8 gigabyte of RAM.  This is attached via Fiber to an EMC Clariion
solution. Our current database is around 250 gigabytes big (including the size of the index files) and has averaged
about60 gigabytes of growth per year.  We have around 200 concurrent users that heavily utilize the database. 

  We are currently in the planning stages of our next generation database system.  We expect dramatic growth in the
comingyears and would like to design a database solution that will last at least 5 years.  Within two years, we
estimatethat we will have around 500 concurrent users and estimate that our database will grow to around 500 gigabytes.
Within five years, we estimate that we will have around 1000 concurrent users and estimate that our database will grow
toaround 1 terabyte. 

  The major concern we have is that we expect database activity to increase dramatically over the current utilization.
Besidesthe planned increase in the number of employees, there will also be increased database resouce utilization per
employeeas management is pushing to increase performance per empoyee and increased data analysis to measure the success
ofthe business.  So it is very important that we implement a solution that can scale well. 

  This will be a rather enterprise quality solution.  On the hardware, we are leaning on either an EMC or NetApp SAN
solution. For a database, we plan to either deploy RHEL as it provides migration from AMD64 to Itanium/Power or Solaris
asit provides migration from AMD64 to Sparc.  On the database end, the possible options include Oracle, DB2, Sybase, or
PostgreSQL. We would prefer to go with PostgreSQL due to the dramatic cost savings we can achieve.  We have come to
discoverthat as expensive as the hardware/OS solution is going to be, the commercial database costs will dwarf those
costs.

  As this database will be our core database and our entire world-wide branches will be completely dependent on it, we
willneed to make sure that it can perform, scale upwards, and provide high availability features.  I already know that
PostgreSQLprovides high availability.  The other two, I am uncertain.  Will PostgreSQL be able to handle this job?
Whatdo we need to look out for if we are to do such a deployment?  What is the largest database someone has deployed in
production? Largest table?  Any help with this situation will be greatly appreciated.