It turns out that the plugin was installed after all. However, it still doesn't permit me to play these WMA files I bought from BuyMusic.com. It seems they're copyright-protected somehow. They play on Windows Media Player and Real Player, but not on most other software players. Curiously, they will play on an old version of UltraPlayer. I'd like to play them on XMPlay, if possible, but maybe the scheme can't be defeated.