Pompeii was devestated first, although it was first covered in a layer of pumice and lapilli, and herculaneum wasn't so much affected. But, Herculaneum was destroyed pretty much instantaneously from a pyroclastic flow, it just charred anything and everything. The remains at Herculaneum are preserved better than those in Pompeii, this was due to the fact that the volcanic material was lighter and allowed oxygen to reach the remains, whereas the remains at herculaneum were covered in a much more dense and muddier volcanic substance and kept everything preserved better.
i hope this helps someone.
also look at 'secrets of vesuvius' by pamela bradley. you can get the book at dymocks.:wave: