I'm pretty sure the Creative SB0670 (X-Fi XtremeMusic) is a PCI card - not PCI-E. The difference is easy to see by looking at the slot-connector, it's much wider on a PCI card.
X-Fi XtremeMusic (SB0670) card:
PCI 2.1 cards should be backwards compatible with PCI 2.0 motherboards, unless the card/driver needs a specific PCI 2.1 feature.
There seems to be a lot of problems with the older X-Fi cards on Windows 7.
I think you should uninstall the driver in Device Manager:
Open Device Manager and find your soundcard under "Sound, video and game controllers". Right-click and choose "Uninstall".
When confirming the device uninstall - tick "Delete the software for this device".
Then go to Control Panel and uninstall all Creative software.
Turn the computer off (not restart). Disconnect the PC from main power, then move the soundcard to another PCI slot.
Start the computer and let Windows install a driver automatically.
When/if the sound is working you can always use a third-party mixer to optimize the sound.