Downloaded and burnt 'ReactOS-0.4.1-REL-iso'.
Machine: Asrock K7S41GX (http://www.asrock.com/mb/SiS/K7S41GX/)
Installed on hard-drive perfectly.
On boot up hangs. Note debugger doesn't accept any input. Rebooted several times same result.
Since switching off everything USB in the BIOS Reactos boots lovely. When I get time I will test some other hardware. Once the USB stack is fixed I'll give it another try. At least I'm up and running on real h/w.