Hello from PP!
The Vietnam rules are now in PDF form as well as print form. The PDF version is £9.00 GBP. The PP website gives detail of game mechanisms and other data.
In short: The rules use a gridded table – 5x3 for 15mm, 6x4 for 25mm etc… The grid grows for 25mm and larger figures. It shrinks for 10mm and smaller figure sizes. The rulebook includes search-and-destroy, firebase, mountain tribes, downed aircrew, etc. scenarios. In 15mm, you will need a platoon of white star (U.S., Australians, ARVN, etc.) and a platoon-plus of VC or NVA. In 54mm, you can use one figure per base, thus needing about 25 white-star figures for a game.