performance optimzations

I'm moving a webmail service over to use a postgresql database for
storage and wanted to get any tips for optimizing performance. The
machine will be a multiprocessor (either 2 or 4 cpu ) system with a raid
array. What layout should be used? I was thinking using about using a
raid 1+0 array to hold the database but since I can use different array
types, would it be better to use 1+0 for the wal logs and a raid 5 for
the database?

The database gets fairly heavy activity (the system handles about 500MB
of incoming and about 750MB of outgoing emails daily). I have a fairly
free rein in regards to the system's layout as well as how the
applications will interact with the database since I'm writing the
code.

--
Suchandra Thapa <s-thapa-11(at)alumni(dot)uchicago(dot)edu>