Hardware and OS for postgresql

Hi all, my question is related to two recent posts, which didnt quite
answer my curiosity.

(1) Scaling in which direction will help postgresql best, given the
queries are CPU, memory, io and disk-intensive? I understand dual-CPUs
will help in certain circumstances, but say for large subqueries which
are built in the memory, will it help to have a server in which there
are memory segments dedicated to each CPUs? In this regard, does
anyone know of a specific Sun Ultra, RS/6000 HP or Dell  server whose
architecture is especially favorable to Postgresql or databases in
general?

(2) Our company has an ERP system running on MS SQL server on an
xSeries. The total database size is 1.8GB and its very IO intensive
with about 25 concurrent average users (60 max). I'm planning to run
the same database under postgresql on a measly Sun Ultra5 or RS/6000
7043-140, with 512Mb Ram, Ultra2 SCSI disks and gigabit ethernet to
provethe benefits of Linux/BSD/UNIX/pgsql. Will a default install of
pgsql 7.4.2 do the trick? Will adding more Ram or CPUs with fatter
caches help more?

Or am I way out of my league trying to run this database under such
specs?