How I open MPC in WMP11 Beta?

Do you mean play Musepack files in Windows Media Player 11?

I don't think it's possible.

EDIT: oops, I didn't know about the DirectShow filters

See the last item on this page:
http://www.rarewares.org/mpc.html

Or, alternative links (and newer version, it seems):
http://www.radlight.org/products/filters/filter.php?filter=7
http://www.free-codecs.com/download/RadLig...Show_Filter.htm

You probably also want to install the tag extender if you want the files to show up in the media library:
http://wmptagext.sourceforge.net/

But there really are a lot of better programs than WMP out there, you can start with this list:
http://musepack.net/index.php?pg=pro

Tks guys!
Mr_Rabid_Teddybear, WMP Tag Ext. haven't worked properly here... i dont know how to add MPC files to the WMP11 Library.

Well, I'm not actually using WMP, just thought tag support could be nifty to have if you are. However, the developer has a thread on this forum, so if your experiencing problems, you should take it up with him...

thanks, Mr_Rabid_Teddybear! You have helped a lot!