HelolW rdlo (A threading challenge)
C, 61 62 chars

i;main(){write(1,"Hello World\n"+i++,1);i&gt;13||fork()||main();}


The pthread library functions all have loooooong names, so instead I fired up an entire separate process for each character. fork() is so much shorter.

It was necessary to use write() instead of putchar() because the stdio buffering functions are not thread-safe.

Edited: Back up to 62 chars. In my zeal, dropping down to 61 chars also dropped the thread-safety.