(in the meantime, still wondering about persistent ratings .. had the drive letter change due to O.S. reinstall and lost em all .. again)
The PortableApps.com version of XMPlay uses a wrapper around the program and makes the drive letter modifcations to the files as needed. This is great for people using XMPlay from USB drives or external hard drives since drive letters change frequently.
While it probably isn't ideal to permanently use the portablized version on your local hard drive, it may fix this problem. Download and run the portable program once without any data, then copy your "broken" library, pls, ini, and your "stuff" version of XMPlay.exe over the corresponding files in the \Data directory, and then run again. It should edit the files to make the drive letter changes. Then copy your "fixed" files back to where they came from.
Edit: some stuff is in the \Data directory, some in the \App directory (like the exe).
Here's the link:http://portableapps.com/apps/music_video/xmplay_portable