how can I copyright my writing on myspace?
Any original work you create is automatically copyright. You don't need to do anything, though if you want to be able to prove you were the creator, you may want to do something to prove you wrote it first, ranging from posting it to a site to having a copy signed and dated by a justice of the peace or attorney, or posting it to yourself in a registered mail envelope (and _not_ opening it when you get it back!)
(c) try that
Or just type copywrite...
but I dont think you can actually legally do it...so just use (c)