ia32-libs : Depends: ia32-libs-i386 but it is not installable

I am trying to install ia32-libs (a dependency to build the VirtualBox sources) on my Debian x86_64 box, however it's giving me the error:

The following packages have unmet dependencies:
 ia32-libs : Depends: ia32-libs-i386 but it is not installable
E: Unable to correct problems, you have held broken packages.

Naturally, I went ahead to try and install ia32-libs-i386, but I faced another error:

Package ia32-libs-i386 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'ia32-libs-i386' has no installation candidate

Does anybody know what the issue is here? I think I may need to enable multiarch, however I'm not completely sure. Here's my sources.list, if it helps at all:

deb http://ftp.us.debian.org/debian unstable main contrib non-free
deb-src http://ftp.us.debian.org/debian unstable main contrib non-free

deb http://security.debian.org/ testing/updates main
deb-src http://security.debian.org/ testing/updates main

Solution 1:

You need to enable the installation of i386 packages on your amd64 system:

dpkg --add-architecture i386
apt-get update

The ia32-libs-i386 package is only installable from the i386 repository, which becomes available with the above commands.

See also: http://wiki.debian.org/Multiarch/Implementation

Solution 2:

The problem is using debian unstable and testing. Either use stable (or squeeze as it is currently called) or live with the brokenness.