Actually the trial version in the 6.x line of Hal is fully functional, just limited to 31 days. Speech recognition should work if you have a speech recognition engine installed (one is not included).
Are you saying that you can't hear Hal speak or that Hal can't hear you speak? If Hal can't hear you speak be sure to click on the microphone button to enable speech recognition. If you can't hear Hal speak, try selecting a different voice in Hal's options and be sure to run the Haptek SAPI config program. Check your windows sound level, vista has a seperate control for every program, make sure Hal's slider is up.