oh ok... I have a nforce 3 motherboard myself (MSI), and it works fine on my system. However, that doesn't necessarily mean anything since southbridge configurations (responsible for communications) are usually different between different models/brands.
If you still can't get it to work after an OS re-install, maybe you can try an inexpensive usb pci 2.0 card (buy somewhere where you can return it)... this seems to work well for a lot of people. Also, if you haven't already, it would be good to test your Slimloader on another computer, just to make sure it's not defective or anything.
BruceG