You need at least 3 files to start NetBSD/hpcarm.
iPAQ: ftp://ftp.NetBSD.org/pub/NetBSD/NetBSD-3.0/hpcarm/binary/kernel/netbsd-IPAQ.gz
Jornada 720: ftp://ftp.NetBSD.org/pub/NetBSD/NetBSD-3.0/hpcarm/binary/kernel/netbsd-JORNADA720.gz
This is probably the easiest way, for now.
Connect some device to the serial port. Use 19200bps, no parity, 8bits.
Prepare a DOS-formatted memory card, and copy the above 3 files (currently only 2 files) onto the card.
Insert the card into your WinCE machine.
Checking: did you connect the serial cable already? The serial cable MUST be plugged into WinCE machine before starting hpcboot.exe.
Go into "Explorer" (not "Internet Explorer"), go one directory down to your memory card (the name of the memory card differs by localization), and invoke hpcboot.exe. Alternatively, you may want to setup autoboot, if your WinCE product allows you to.
In hpcboot, setup the following items.
"kernel" screen:
Pray. Tap "boot" at the bottom. You will see "Last chance: Push OK to boot" dialog. Tap OK or return (obviously). If you are successful, you will see boot message like this on your serial port. Congratulations!