I don't use WMP to play my MP3's via wifi. I use GSPlayer. GSPlayer offers a whole lot more functionality than WMP IMO and it is free. When using Resco File Explorer to map your shared folder to a folder on your PPC, using GSPlayer to create a playlist using your shares is a snap. GSPlayer also supports shoutcast which is a plus.
You can find GSPlayer at
www.freewareppc.com.