Hi, I had this problem too. Running Vista Ultimate x64, with X-Fi Fatal1ty PCI-E. I had my speakers set to quadraphonic, since that is what I actually have. Works fine for every other app, except CoD:WaW.
Searched for a way to get it to work in Alchemy, no go.
Found this forum.
Lowered KHz, no go.
Tried forcing the sound in the console, no go.
While playing around in the CoD console, however, I noticed there were two settings: snd_force71 and snd_force51, but there was no snd_force41. Light bulb goes on.
I go to back to the control panel and set the speakers for 5.1 sound. Have not tried this before, so I was expecting to be disappointed since I don't actually have a 5.1 setup. No separate subwoofer or center channel speaker in my possession. However, you can tell Windows which speakers you actually have, and it will compensate by downmixing. So I clear the subwoofer and center channel speakers. Quadraphonic 5.1, or 5.1 minus 1.1? Whatever. Either way, it should be exactly the same as running in quadraphonic, like I was before.
But... CoD:WaW now works with proper surround. Seems a bit silly to have 5.1 channels downmixed to four and have it work rather than just output four channels, but whatever. Silly programmers.