Intel Core 2 Duo vs Dual-Core Xeon; x64 OS

I'm trying to find out what the basic differences are between the
normal workstation-type processors (Core 2 Duo, Extreme) and the
comparable core-count Xeon chips. Xeons appear to be oriented to
server use; why is that?

I'm looking into getting a new machine. This is not for gaming; it is
for my main development/daily use machine where I run 20-30 apps
concurrently all day long, including file sharing, compilers, music
playback, disk backup, photo editing, and more. Dell offers machines
with both Core 2 Duo and Dual-core Xeon.

I also am considering the new quad cores available. I think they would
perform well for my use.

To be sure I'd get the most out of these processors, I'd want 64-bit
support so I'm planning on XP x64 (I will NOT do DRM with Vista).
Linux is only an option if a Windows virtual machine will work on it.
I don't have time to fool around with it. Are programs generally
compatible with x64, or are there issues?

Advice and/or references appreciated!
thanks
tbone

The core 2,s are cheaper i think... Well wikipedia states this:
"Intel released relabeled versions of its quad-core (2x2) Core 2 Quad
processor as the Xeon 3200-series on 7 January 2007.[6] The 2x2 "quad-
core" (dual-die dual-core) comprised two separate dual-core die next
to each other in one CPU package." http://en.wikipedia.org/wiki/Xeon#Quad-Core_Xeon