I'm afraid not. There have been simply too many reports of crashes. And I have been able to make the editor crash myself, on XP fairly easily. I cannot in good conscience release software that I know to not work well.
If you really, really want to run calibre 2.x on XP, you can still do so, by running from source and simply commenting out the code that prevents calibre from starting up, which is here:
https://github.com/kovidgoyal/calibr...init__.py#L925