It seems the build instructions for vb 2.1.x [1] are missing one dependence for the debian apt-get install command: g++-3.3 (as for my ubuntu hardy).
The system on which I'm installing it is quite new, and I believe the g++ version installed by default is the g++-4.2.
After installing the g++-3.3 package, everything went fine for me.
Thanks for the good work team!
[1] http://www.virtualbox.org/wiki/Linux%20 ... structions
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ephrelm