CentOS - Jul 2010 - Help: Please help me size my server requirements

I am looking to build a Workgroup Server. (Should be
compatible/certified with both XEN & VMware hypervisors, as I am not
sure which one I will settle with...comments requested)

To run baremetal on hypervisor, with each of the following services
running virtualized with minimum OS install (CentOS 5.x, latest stable
release).

- Multi-homed router-cum-border firewall (Access to Network Card
limited to this instance...will act as router for rest of virtual
machines).
- DNS Server (djbDNS).
- Mail Server (Qmail).
- News Server (INN).
- Webserver (Apache).
- RDBMS (postgreSQL...highest load).

In addition to above the server to provide Windows RDP &/or Linux
Desktop Thinclient to 5 users running diskless thin clients or old
desktops (second highest load).

Server to have adequate amount of memory for the above and 500 GB/1 TB
RAID 5 or better using SATA disks.

What Server Specs. I am looking at? I understand DB load is major in
this but assuming moderate to medium db load, what do I need. Will
seperate the server & Thinclient server six months/year down the road.

What budget? Recommendations for a processor/motherboard/ram/disks/sata card?

With best regards and thanks in advance.
Sanjay Arora.