When I was starting using QEMU some time ago I wrote, what I was missing (information on how to use QEMU). See http://html.szaktilla.de/qemu ff.
If you want to use Arduino in QEMU you need to "forward" the USB device to QEMU. Since I had some trouble doing this I added an paragraph to my (german) documentation (http://html.szaktilla.de/qemu/9.html end of page).
I'd appreciate if someone could proof-read this paragraph and let me know if something's wrong.