hm. i haven't toyed with mines yet, but i might be able to help clarify the question. what command (interface button, whatever) do you use to lay the mines? 'drop cargo' didn't seem to work. is there a 'lay minefield' or do you need to use a launch button or something?
to answer one or two of your other questions, yeah, there are boarding parties and fighters in the demo. i've researched them and fiddled with the construction of them, though i've never used them. (i whip up on the computer too hard, so by that time i'm just researching to pump my score.
when you start a new game, one of the options somewhere about new races is 'tech level' if you set that to the top, then you start with all the tech available in the demo, and can at least look at all the stuff you've been missing.
