"IRQL_Not_Equal_Or_Less"
Microsofts direct response to that BSoD is that it has to do with software implimintation of how the hardware drivers are being references and used.
Microsoft Technical Documentation
More Microsoft Documentation on IRQL
This BSoD is usually due to either an OC PCI bus or bad drivers. (I use to get this a lot). If you are currently OC your FSB, then drop the FSB down a few units and see if the problem corrects itself. Since your MB is using the VIA KT400 chipset, got to
www.via.com.tw and download the lastest chipset drivers and install them. Also check to see if you have all the latest drivers for all your devices in your machine and update them as needed.
If all of the above does NOT eliminate the problem, then definately consider reinstalling Windows and/or looking for a newer PSU.