THANKS for the heads-up, dwell. I was a bit skeptical when I read on the nomadworld page that wma "provides unsurpassed audio quality, with CD-quality sound in half the size of an MP3 file". Well, I listened to my first .wma file at 64kbps and it sounded pretty good, I must say.
And yes, it looks as if long (or at least longer) filenames are supported. I transferred a file and didn't get the truncated filename with the ~ tilde. It didn't display the entire filename because it couldn't fit on the display, but that's fine. It also seems as if wma files are uploadable.