Did anyone give you the impression this should work? When it comes to WMP, all bets are off as it's author had other ideas such as Zune and their store.
But I digress. Did you try MediaMonkey? And yes there are Star sync issues there. I can't recall if they support the half star sync.
My Creative Zen lets me rate songs via 5 Star ratings just like Windows Media Player. The problem is that those ratings don't sync back to Windows Media Player. I have way too many songs to sit and rate, so while I am listening to music on the player, I like to rate the song. How do I get those ratings into Windows Media Player?
I am looking to buy a new player so if I can find one that tags the song with that rating, and then even overwrite (or sync) what's on my computer, that will work too.