Have you tried either 1 double checking the connection protocols that are installed, verified that there is no conflict for resources in the hardware menu.

If not try that, if that doesn't work, uninstall the driver, and then *before reboot* fully remove the driver from windows (get the names of the drivers from the hardware menu and actually delete the ones from nVidia), then reboot, then install. I had to do this MANY times in Win98se (after getting rid of MS Windows Mistake Edition due to it having more problems then features with my hardware and software).

You can try to go into the BIOS and clear the configuration data (ESCD), and then boot, but this may cause other resource confilicts which can be fixed by removing every I do mean every device from your hardware menu, just save the video cards for last, then reboot.

Linux shouldn't mess with your hardware in such a way, If you don't attempt to screw with it from Knoppix then it won't screw with Windows.

P.s. I have a Asus a7n8x delux mobo with the Nforce2 chips, and last I checked only the integrated 3Com nic that the Asus put on worked with Knoppix... How did you get yours working without installing the drivers, or are you using another varient of Knoppix?
Note: I havn't messed with my nForce Nic for around 4 months worth of Knoppix builds.