After a couple of tries, I got the disk image ready and partitioned. Whenever
cfdisk hung QEMU, I had to kill the emulator and restart the process. I found
that the changes that were successfully written to the disk image were good,
so I was able to make forward progress.
I have installed a complete debian.
I have had the very same problem: sometimes qemu freezes.
There is no apparent cause-effect relationship, qemu freezed at random
stages of the installation process any time the procedure was restarted.
I succeeded in installing the debian but after several attempts.
It seems to be a timing fault on the simulated ide.
When it freezes, it stops into a low level infinite loop: neither
clicking on the window to grab the mouse nor ctrl-c on the calling
terminal produce effects.