A scripting language such as ruby or Perl could be used to easily do this. They offer connectivity to most major DBs too. In fact you can just outpt to a CVS file and then import using the DB import tool you have (all databases come with one).
I once wrote a Perl script to do this type of thing and rather than just using it once I maintained it over a few weeks and it turned into a powerful data generation tool in which you specified the the number of rows required and a desription for each column which determined te weightings of the data. It allowed it to generate more realistic data (for an analysis tool).
In the end it was used to create a 70 million record data set. If I had it handy I'd add it here!