The newest thread on the Sibelius forums mentioning running Sibelius in Linux is here:
http://www.sibelius.com/cgi-bin/helpcenter/chat/chat.pl?com=thread&start=189898&groupid=3&&guest=1
Sibelius Software has stated in their tech support forum that they won't be making a native Linux version any time soon. Sibelius 2 has been reported to work under Win4Lin (except MIDI & audio), and Sibelius 3 runs successfully with VMware.
I think that Wine and CrossOver would be a superior way to run Sibelius in Linux in this situation. It would be great if Sibelius Software became active with this, but maybe some progress can be made even without them.
Even missing some features (say, MIDI/audio) Sibelius would be more useful for professionals than the current free/libre/open source alternatives which run in Linux.