I imported them, and they show a greyed-out icon. I get the "unable to play any files in playlist message) They're not filtered in any way. I don't even own an iPod (I'm such a Philistine). Maybe you need to own one to make this work?
Ok, I just did an end-around experiment that successfully played these tracks, though I have no idea what made it work, I can tell you what I did:
Instead of right-clicking from explorer and sending to MC, opening from MC, or importing from MC (all things previously attempted), I went through the internal MC My Computer tree and went to the folder that contained an iTune downloaded album. MC spun its wheels for about a minute while it was gathering info on the files, and sure enough the icons were now showing playable and they play with no problems (and sounds far superior to iTunes' jukebox with the MC's DSP FX).
Still no theories on what difference going at it that way made, but as soon as I actually have some more iTunes downloads to try I'll see whether this is something that will occur every time, or just the first.