1. Disable the network ports in BIOS. You can find them under 'Onboard device configuration' in the 'Advanced' menu in BIOS.
2. Uninstall all nVidia devices from Device Manager (right-click on my computer, properties, hardware, device manager). Don't let the system restart (say 'No' to any automatic restart requests).
3. Uninstall all nVidia software from the Control panel.
4. Restart the system in safe mode
5. Delete all files beginning with nv in the C:\windows\system32
6. Open this directory: c:\Windows\inf and start opening the files named oem0.inf, oem1.inf, etc. Delete the files which relate to the nVidia hardware. You can read which hardware device the file belongs to, in the first few lines of the file.
7. Reboot and see if you're still getting BSODs. If you are, the problem is a general hardware failure, either of the modem or the chipset southbridge. If the BSODs stop, it's time to install the drivers again.
In case the latest drivers don't work, try a few of the older ones. Sometimes new drivers (the latest is Nov 2006 for this board, btw) may break the system.