It's not that hard, even without a truing stand. Take the wheel off, take the tube and tire off thw wheel, unscrew the offending spoke out of the nipple. Find a spoke of equal lenght (when I say equal, I don't just mean for the same wheel size, but when you stand them up next to each other, they are exactly the same). If the spoke you took out broke somewhere away from the ends, you may need to take out another spoke to get the appropriate size. When you get the right spoke, reinsert it through the hole in the hub, and thread it so the pattern looks the same around the wheel. Don't be afraid of bending the spoke a little, it'll straiten out when you tension it.
To true the wheel, mount it back on the bicycle, and mount the bicycle somewhere where the rear wheel isn't touching the ground. Pedal, and find where it looks out of true. Here's the trick: when the wheel wobbles one way, tighten the spokes that start on the other side to pull it that way.
Hope that helps.