This problem is really starting to bother me. It only really happens when I am playing Oblivion. Sometimes when I try to enter a building my computer basically vomits and flashes a blue screen then I have to reboot. The blue screen says the following:
Driver_Irql_not_less_or_equal (at the top of the page, then it follows with this tech info)

Technical info
***STOP: 0X000000D1 (0X0000000B, 0X00000002, 0X00000000, 0XF674A708)
***portcls.sys - Address F674A708 base at F6749000, Datestamp 41107F13

I really have no idea what this information means though I know it is important. I have all my drivers up to date I use a program called DriverAgent to make sure of this and I have had good results with them in the past. I made sure to install my drivers all in the proper order as well so I am pretty sure that is not the issue. I tried to assign irq values to all my periphials in bios but that didn't fix it so I put it back on default. When I look in my device manager there are no red X's on any devices nor are there any yellow ? marks. I have spent alot of time building this computer and this has got me at my wits end. Oh and no I did not install the firewall that comes with this motherboard, as I know it has issues. If anyone knows how to read that code or can point me in the right direction to someone who does it would be greatly appreciated.

portcls.sys is a audio device file
check that you have the onboard sound disabled & if your Audigy is sharing IRQs at all.

Oblivion is a sweet game but full of bugs.

One question and one possible solution...

What graphics cards are you using? Single or Multi?

One thing I suggest you look at is the BIOS setting for the NB to CPU (Northbridge to Processor)and the SB to NB (Southbridge to Northbridge). They should BOTH be 5x and 16 bit down / 16 bit up. In total there should be 4 settings you should make sure are at full speed. I have been seeing sync issues on other platforms with this ... this seems to fix part of it. Perhaps it will help here.

onboard audio is disabled, but I suspect the problem may be with the soundcard like you suggested, will look further into it.

Oblivion is sweet, but it crashes when I try to load a game that was saved inside of any structure, whether I'm in a cave, or a house, or a castle, it will crash. If I can see the sky when I save then it works fine. I played the whole game this way, beat it on day 300 gametime so I guess that hotfix worked fine for me. Just a pain in the ass to run a dungeon with no quicksaving. Anyway to answer your question yes I am in SLI check my sig for pc specs. I hunted all through my bios setting in vain looking for any setting that said anything about Northbridge or Southbridge or their abreviations. My instruction manual that came with the motherboard made one brief mention to Northbridge which looked like this:

* DRAM Command Rate:

When the host (northbridge) locates the desired memory address, it then processes the wait state of commands.*

I really have no idea what this means. I consider myself somewhat computer literate but I have failed to make a connection on this subject. Would you mind going over NB and SB options and what they do and where I should be looking?

Ok I investigated further into my Device Manager and looked at every single device listed to check for IRQ conflicts. It seems both my Network Bus enumerator and my Standard OpenHCD USB Host Controller are using IRQ value of 21 with no conflicts reported and no option to change the IRQ through the Device Manager. Also my Nvidia nForce PCI System Management reports a conflict in it's I/O Range, this reads like this under the Conflicting device list:
Input/Output Range 1C00-1C3F not available.
Input/Output Range 1C40-1C7F not available.

There is no option to change these addresses in this screen though. And the IRQ value it shows does not conflict with any other IRQ that I could see.
How do I fix these errors?

ACKKK! Another crash! This time it is not while playing Oblivion but while trying to set up my Home Network. The Connection Wizard causes a Blue Screen of Death and requires a reboot to recover. This blue screen error reads a little different. It still says "DRIVER_IRQL_NOT_LESS_OR_EQUAL at the top of the page, but the tech info code is a little different and so is the filename it provides, it reads like this:

Technical information:

***STOP:0X000000D1 (0XA00000EC, 0X00000001,0XB95098D4)

***HTTP.SYS - Address B95098D4 base at B94F8000, Datestamp 41672744

I can repeat this error over and over, and it is preventing me from connecting my Home Network. I am fresh off of a recent format and have triple checked my drivers, they are all up to date. Please help!

when loading the nVidia chipset drivers do not load the Network Access Manager

Damn, I had heard it was only the Nvidia Firewall that was full of bugs. Is there any way to uninstall the Network Access Manager without a format? Nevermind, I am formatting anyway.

OK I uninstalled the Nvidia Network Access Manager through my Control Panel Add and Remove Programs. This allowed me to install my home network without crashing. But in my device manager I still see the Network Bus Enumerator and Standard OpenHCD USB Controller are still sharing the same IRQ value with no errors reported. And the Nvidia Nforce PCI system management still has conflicts in it's I/O range, read earlier post in this thread for details on that error. I am going to play Oblivion for a couple of hours to see if it crashes.

the Network Access Manager is the firewall ...

You can install the network access controller without using the option for the firewall. I did.

Does anyone know how to fix these conflicts?