Finished it. Not a whole lot useful to my game at present, but I got to see a few more of the tools in Vassal.
I was very unimpressed by Virtualscape, to be perfectly honest. The interface is a pain and I can't easily edit large areas, only individual pieces (or everything at once). The shapes you can use are based on the plastic pieces you get in Heroscape, so they're not as customizable I'd like for designing other games. I messed around with it for a while, but couldn't get it precise enough to be able to create the map for my game, so gave up on it.