Use Windows XP sounds in OS X?
You technically can't replace the sound files as they are protected by SIP (well... you could by disabling SIP, but that's another discussion altogether), but you can add sound files to your own personal library.  This is much easier to do.

There's basically two steps to this:


Convert your WAV file to AIFF.  
Copy the file to ~/Library/Sounds (Note that this is located in your user directory and not the SIP protected /System/Library directory).




The easiest way to do this is to use FFmpeg1  Just issue the command ffmpeg -i &lt;path&gt;&lt;name of file&gt;.wav ~/Library/Sounds/&lt;name of file&gt;.aiff and it will do both steps in one shot.

The nice thing about using FFmpeg is that you don't have to manually open each file in QuickTime as you can do it right from Terminal.  This also means you can write a quick batch file to do all your sounds if you like.


Once you do that, it should show up in Sound Preferences as a "Custom" sound (I created an "Ask Different Sound" specifically for this example).  Be sure to completely close out of System Preferences (if open) before going into "Sound" so that it can load up the new files.





1  FFmpeg is open source, free software that converts almost any audio/video file from one format to another. Simply download the binary and make sure it can be found in your path.  I just copied it to /usr/local/bin so I didn't have to modify my path at all.