For the problems with WMP12 that's a quick fix! Before it will simply play any form of media you have to go through the setup and make that the default media player for the initial run. Later when adding another player and made default WMP will still play media. The rest is what codecs are still needed after you perform the initial setup.
Once you pass the "made wmplayer the default media player" screen it will perform a system scan for all media files which includes the wav files found in the Windows>media folder for assigning sounds to various functions.
Recognise that little startup sound when first booting into Windows? Once WMP is setup you will then start hearing that unless unchecking the play startup sound box found in the Control Panel>Sound>sounds tab there. Once all that is done you should able to go into the media sub folder in the Windows directory and double click on any wav file to hear that or see any audio or video file start WMP when double clicked on.