Ideal web server configuration

[Mike Leahy]

Hello list,

I'm looking at ordering a new web server for the office I'm in, and I'm
wondering if anyone has any suggestions regarding the hardware that I
should choose.  Normally, I've worked with hardware that was already
available to me, so I've never really had to put consideration into this
upfront.  I know this may be a bit off-topic for this list, but I figure
people on this list will likely have some experience with this.

The application we're working on will involve multiple simultaneous
users interacting with a chameleon-based map interface.  The
communication between the client and server will generally involve AJAX
requests and downloading of updated map images generated by MapServer.
On the server side, we'll be running Apache, PHP (with MapScript), and a
PostgreSQL/PostGIS server that will be receiving frequent
queries/updates.  There will likely be some high resolution imagery, as
well as a variety of vector layers used in the map that is displayed.

Given that I have a relatively modest budget to work with, what I'd
really like to know is how I should prioritize the different hardware
specs that I can choose from (e.g., multiple CPUs/core, RAM, SATA/SAS
and/or RAID disk configurations, etc.).

Thanks in advance for any suggestions,
Mike