Do you have to have the board game to use VASSAL? If not, how do you get it to work? I loaded a module of N Africe from the Europa series but couldn't figure out how to move a single unit from a stack. Doesn't appear to be real user friendly. Would be nice if it was and they did a lot of the old big SPI games, which I saw a list somewhere that they were working on.
You don't necessarily need to have the board game however, you do need to have the board game rules. The reason for this is that Vassal does not have an AI. The program will allow a player to move units (counters) all over the place with no restrictions, so it is up to the player to know the rules.
Most SPI games are not supported by Vassal because Decision games does not allow Vassal to host their games. Vassal also does not support Avalanche games and GDW for the same reason.
It does help to have the board game...(like it was said above at least for the rules)..I have tried to be an observer to other games so I can learn but not with much success...