Any of you budding musicians know of any very basic music composition software, either online or free download...
When you say keyboard, you mean musical keyboard right ?!
Erm then no.
Guitar players can use guitar pro to lay tracks - not sure it has "keyboard" as an instrument though (edit, it looks like it might, the RSE has piano), and it almost certainly won't take a midi/keyboard input and auto score it: http://www.guitar-pro.com/en/index.php
Oh and its multi format but not free...unless you, well you know, I would say but would expect a
torrent of abuse