Is the Sibelius offered on Tapspace compatible with Ubuntu or Debian? Both of Linux distros that I have running on two desktops.

No, it only runs on Windows and Mac OS.  There have been people who have successfully run Sibelius 4 using Wine on Ubuntu and other Linux distros, and some have halfway run 5, but there's no support for either one.  Hence, you'd be completely on your trying to figure out what sort of dependencies would need to be satisfied in order to even have a remote chance of the program even starting.

Good luck :-)

Linux could be awesome for music- but no one supports it.  There are virtually no professional or consumer audio applications or hardware driver support for it.  It seems no major player in the music industry is willing to make the leap. 

Indeed, Jesse - especially since Mac OS is based on Unix anyways. The JACK stuff is decent, but it pretty much stops there, unfortunately.

[quote author=J Mattson link=topic=3417.msg18095#msg18095 date=1259975657]
Linux could be awesome for music- but no one supports it.  There are virtually no professional or consumer audio applications or hardware driver support for it.  It seems no major player in the music industry is willing to make the leap. 
[/quote]

Nothing anyone's heard of anyhow. I heard of a music school that only teaches their students the free linux music programs. Forgot who it was though.

http://www.linuxlinks.com/article/20080622143124178/Audio.html

http://en.wikipedia.org/wiki/List_of_Linux_audio_software

http://en.wikipedia.org/wiki/List_of_free_software_for_audio

I fooled with Rosegarden a while back, and for what it's worth it's not terrible.  It could easily be just as good as the other mainstream stuff if it was a commercial product.  Not bad for open source notation - and you can't beat free... sometimes.