I think the question is not that he wishes the computer to understand him, but rather he wants the computer to emit his voice instead of the standard windows startup sound.
If that is the case, then you are most of the way there in that you recorded your voice to a .wav file. All that remains is to assign that .wav as the sound for the desired system event. To do this, go to Start:Control Panel and double click the Sound icon. This will bring up the Sound dialog.
Click on the Sound tab at the top and you will see a window listing the Program Events which windows has sounds for. Click on the desired Program Event (in this case it would probably be Windows Logon), and then click the Browse... button below. This will bring up a windows explorer window where you will need to navigate to your recorded .wav file and select it.
The next time you Logon, you should hear your recording.