The harddisk of my aunt’s pc was broken, and I had an old disk around that I could use for replacement. Now I wanted to install it prior to go there. Of course there is the option to take my harddisk out, and use my PC to install her harddisk. But I wanted to use my machine for other things during that time. So I checked, if I can configure VirtualBox to use an external harddrive connected with an IDE to USB converter. I didn’t find such an option. So I read up a bit on qemu. I used qemu before, and quite liked it. Qemu is fully commandline which is cool sometimes, while other times I like to have a GUI such as with VirtualBox. This time it didn’t matter, I only needed to be able to install an iso onto the external harddisk. And it’s as easy as this:
sudo qemu -boot d -cdrom ~/Downloads/linuxmint-12-gnome-dvd-32bit.iso -hda /dev/sdc -m 512
The sudo is only required because as a regular user I don’t have write permissions on /dev/sdc.
edit 5.Aug 2012:
On Ubuntu 12.04 replace qemu with qemu-system-i386 or qemu-system-x86_64