After a fresh Windows 7 installation, you sometimes find your PC having a raging battle with the harddisk. After checking the task manager, you find that some evil process named "wmpnetwk.exe" is eating all your HD-cycles (funny, compared to the term processor cycles, the term HD-cycles is actually more valid, but is never used!).After the usual internet search stuff, I found it's possitble to disable the network sharing of your favorite media player: Windows Media Player 12 (NOT!!!). To do this, go to "Control Panel", "Network and Internet" and click "Change advanced sharing settings...". There, you can select (see figure below) "Turn of network discovery" and "Turn off file and printer sharing" and "Turn off Public folder sharing ()". A bit lower, click "Choose media streaming options".
Then, select "Block" in the bar, see figure below.
All that disables your media sharing stuff, but if you don't use it, it should free up quite some resources.
EDIT: In the end, I found that the service actually keeps on running, even if media sharing is disabled. To really get rid of the annoying .exe, start "msconfig" (start -> run), go to the "services" tab and disable "Windows Media Player Network Sharing Service". You need to reboot or manuall stop the service for immediate effect.