I use ABC for music on linux - with abcm2ps, ghostview and an editor that does syntax highlighting for ABC (many do) and the ABC plux extension for multi-part scores it's pretty powerful.

You can't runs Sibelius directly on Linux - but it seems you can run Sibelius under WINE which is a program that lets Windows programs work on linux with varying (quite good now) degrees of success.

Anahata