How do I filter a voice recording to sound like a NES game sample? The style that I am shooting for can be heard on this video:
http://www.youtube.com/watch?v=nZlPiehYpVM
at 2:18 ("Blades of Steel")

I have tried playing with equalization, hi-pass/low-pass, and various filters, but I can't seem to get anywhere close to this effect, where the "s" sounds come off as static, and the annunciation of consonants is muted (possibly an attack filter?). I can't find any documentation through Google search, either.

I know very little about the sound architecture of the NES, other than that music was composed with Square and Triangle waves, and the "samples" were presented through a separate sound channel. On NES sound emulators I use, this channel is usually labeled "PCM," (Pulse Code Modulation?) The NES system itself was 8-Bit, but I do not know if its sound system was.
You wont get that effect with just an EQ.
try using a bitcrusher effect to reduce the bit-depth to 8 or 16 bits, maybe some saturation and a lowpass at the end to tame some of the distortion.

The characteristics of these old game sounds come almost entirely from the crazy low resolution and data compression necessary at the time to get the samples onto the game cartridge.

good luck!