I'm sure I've read somewhere that he does play piano... I think it was a commentary around writing Desperado - Don played Glenn a couple of bars of music on the piano but at that stage the lyrics were "Leo, my God, why don't you come to your senses..."
If I remember correctly!
Edited to add: well d'oh and double-d'oh, It's from the liner notes of Very Best Of and they're also right here on Glenn Frey Online! Here's the link: http://www.glennfreyonline.com/eagle...linernotes.htm and this is the relevant part:
GLENN: It was only a day or two after we had been back from England with our first album. Don sat down at the piano and showed me this song he was working on, and it was the intro to "Desperado." Originally, it was written for a friend of his whose name was Leo. And so the song started out "Leo, my God, why don't you come to your senses. You've been out ridin' fences for so long now."
To be strictly accurate, it doesn't say that Don PLAYED it at the piano, but that's the way I interpreted it.