My photos aren't terrifically clear, but you can see the two spaceships maneuvering around a central sun (and its gravity well). They shoot at each other, and that's a videogame. The starry background, famously, is based on actual star charts.
The original source code to Spacewar has long been available (here, for example) but it is minimally-commented PDP-1 assembly code and not very accessible. The GAMBIT folks have worked for several months to reverse-engineer the code and figure out what's going on. See their blog posts on the project.
GAMBIT has promised (nudge, nudge) to post their marked-up copy of the original assembly, to document what they've discovered. I'll add a link when that happens.
If you missed Spacewar today, you should drop by the MIT Museum this Friday evening (5:30 pm); the game will be demoed again.
More photos below the dotted line.