I just got skype working on the olpc xo so I thought I'd report it in case anyone else is thinking about doing it. Some other posts made references to it being difficult to set up, but I didn't have much problem. There are basically two steps: (1) download the Static version of Skype for Linux from the Skype website and unpack it with tar. It's not a tcz file, of course, being on the Skype website (to my knowledge no one has written a tcz file for Skype). Then (2) download alsa.tcz with tce-load. I was surprised that it was this easy. I did hit a few snags (mostly involving missing dependencies, I think) but after some tinkering I got everything working and now I have Skype on an olpc xo with microcore as the OS.