Ok I fully understand how both sensors work, I think I'm just not explaining my problem very well.
If you look at the 2 plots that Dave posted, you'll see both sensors will have a voltage output for fuel ratios between 10:1 and 20:1. The wideband is linear, the narrowband is piecewise/shit.
However despite being shit, the narrowband still has a voltage output for any of the fuel ratios, and notice there is ~1 volt difference between rich and lean.
My problem is that my O2 sensor seems to always be reading ~0.2 volts, which is lean. If it were working properly it would at least be constantly jumping back and forth between 0.2v and 1v at idle (ECU doing it's trim thing or whatever). So I assume it's stuffed.
Anyway, there is a new o2 sensor waiting for me at work. I'll plug it in and see if it makes any difference and I'll post up the voltage outputs here.