i had a similar problem on my iMac. i installed Mac OS 9 on it and decided to try out the voice password. It worked well for a while (for a built-in mic that is) but then one time I booted up, tried to log in and said it couldn't find the mic, and made me type in my password. I did the same as you, i even ran conflict catcher and it told me sound manager was the problem. anyway, eventually i did a clean install. To save time though, do a bare install. All you need to do is replace the system file. that fixed my problem and i think it'll fix yours, floogee.
-representa