You could:
consolidate all of the music to one library on one computer (that is always running)
enable sharing in iTunes which will allow any computer on the network to access the library
get an iPod touch/iPhone and install "remote"
-optional run "simplify media" (free) on your computer and iPod touch/iPhone. This very cool application will allow you to access your iTunes library anywhere with internet connectivity on a touch or iPhone
then get an airport express for each room that you want music
consolidate all of the music to one library on one computer (that is always running)
enable sharing in iTunes which will allow any computer on the network to access the library
get an iPod touch/iPhone and install "remote"
-optional run "simplify media" (free) on your computer and iPod touch/iPhone. This very cool application will allow you to access your iTunes library anywhere with internet connectivity on a touch or iPhone
then get an airport express for each room that you want music