After installing the Audigy NX 2 external (USB) sound card on a Compaq 
Armada 7800 laptop running Windows 2000, playing audio files on a 
network drive causes a BSOD with the error driver_irql_not_less_or_equal 
on openhci.sys, the USB driver.  Playing audio files on a network drive 
did not cause a BSOD before installing the Audigy.  Playing audio files 
locally presents no problem.  What do I need to do to successfully 
resolve whatever conflict is preventing me from playing audio on the 
Audigy from files on a network drive?

I've tried:
- updating to the latest Windows Service Pack and all updates
- updating to the latest driver for my Xircom XE2000 network card
- updating to the latest Audigy driver
- uninstalling and reinstalling the Audigy drivers
- disabling the built-in audio hardware
- replacing the network cable
- I've tried using MediaSource (comes bundled w/ the Audigy), Winamp,
and Foobar2000 to play the audio files

I had the same problem with an external USB ADSL modem under windows
XP - this only occurred under boot-up or shut down, so wasn't too much
of a nuisance. The reason why this is under a comment rather than an
answer is that I was unable to find a solution to this - it was only
the modem that generated the BSOD, and it didn't matter which USB port
I used (I invested in a Belkin USB2 card to no avail). Just thought I
would add my comment before you spent more money. Unfortunately, it
just seems to be a conflict with some USB devices. I worked round it
by installing an internal ADSL modem - however, I'm aware that this is
not much comfort to you, with your laptop.

This sounds like a driver issue, we just covered this in my Windows
2000 course at ITT Tech.  Even though it auto sets your Interupt
Request(IRQ, the error your getting is basicly this, every device in
your system has a "number" to identify it, it sends this IRQ to the
processor asking for "attention"), but windows 2000(maybe XP though I
have yet to stumble on this issue myself for XP) has an annoying habit
of everyonce in a while making the IRQ the same on a new device as an
old one had, causing your IRQ problem.  In order to solve this merely
uninstalling the driver and reinstalling(most likely using
plug-n-play) will not work, simply go into the control panel, system,
device manager, and properties of the device with the conflict, under
this look the the IRQ number and change it to one not currently in
use(this may take a while of investigating your systems used IRQ's, I
keep a list of these in documents for my home-network computers.

In most system BIOSes, there is an option to assign an IRQ to the USB substem.
Check in your BIOS for that setting, and try switching it. 
Not: not assigning an IRQ may result in less performance. (Though
slower USB would probably be better than blue screens.)

Put your Audigy on another PCI slot and disable some of the USB ports
(and COM ports) in your BIOS. Because there only are about a dozen
IRQ's, which for a big part are already taken, some devices share
IRQ's. Moving the Augdigy to another slot can solve this and disabling
devices that use another IRQ can also help.

To make sure the hardware isn't broken, try the Audigy on another
machine and maybe also your XE2000.