To test a software build I installed Debian 7.3.0, a.k.a. Wheezy, into a VirtualBox drive. All seemed well except the VirtualBox Guest additions did not seem to be active as a shared directory to the host computer could not be mounted. In Aptitude the necessary guest packages were installed and attempting to rebuild the virtualbox-guest-dkms failed by stating that no kernel source was installed. A bit of investigation revealed that a 486 version of the linux-image package was installed but the 686 kernel headers were installed. D’oh! Seems the Debian installer chose the safe kernel but the dkms package recommends the 686 kernel headers.
I chose to install the 686-pae image and set VirtualBox to enable PAE and I was on my way. It was a bit of a head scratcher for a few minutes.