Linux clusters?

[Ben Browning <benb () theriver com>]

I am looking for a few good resources on building Linux clusters to serve 
as mail farms. Specifically, books.

Ordinarily I would turn to O'Reilly, but "Building Linux Clusters" is out 
of print due to bad response (per 
http://www.oreilly.com/catalog/clusterlinux/ ).

Any suggestions would be highly appreciated in private email, so as not to 
spam the list.

Thanks!

---
   Ben Browning <benb () theriver com>
      The River Internet Access Co.
             Network Operations
1-877-88-RIVER  http://www.theriver.com