I saw your other thread and it mentioned that your WMP is uses 100% CPU when using your extenders. Is that the only time? If so, what are you doing on the extender?
If you are attempting to watch a movie that the extender does not natively decode then WMP is used to transcode and stream the movie to the extender.
Some things that would help troubleshoot are:
1- System specs, this is on option in your profile and helps others trying to help you.
2- OS Build. 7100 and below had quite a few Media Center related bugs
3- What 3rd party decoders, codecs and such you have installed. If you have a Codec Pack...don't! Some play nicer than others but I wouldn't recommend ANY.
I can try to help further if you provide the above. Thanks