I've looked in the forum and historical photograph sections of this site; I've found precious little on pistol crossbows. It even appears there's just one type of modern pistol crossbow sold: http://www.kultofathena.com/product~item~CB1~...ossbow.htm ...There are a number of sites I've found that sell the same product. The information I'm interested in, though, is more historical: When and where was this used?

All I've found so far is a bit of info from wikipedia: http://en.wikipedia.org/wiki/File:ChineseCrossbow.JPG

The crossbow in the image is dated at the 2nd century BCE... would this have spread into the Middle East, or perhaps Europe? Would it have a practical application outside of hunting small game? Assassinations, maybe?

There is a late medieval or early renaissance pistol crossbow in the Banat Museum in Timisoara, Romania. This is not a very good picture but the crossbow is quite interesting.
[ Linked Image ]

Pistol-like grips aren't uncommon among Chinese crossbows:

http://www.atarn.org/letters/ltr_dec00.htm

http://www.atarn.org/letters/ltr_feb99.htm

http://www.atarn.org/letters/ltr_nov99.htm

http://www.atarn.org/chinese/bjng_xbow/bjng_xbow.htm

Note the different internal mechanism of the release, which makes the "pistol grip" design more feasible in Chinese than in medieval/Renaissance European crossbows:

http://science.howstuffworks.com/crossbow.htm

This design doesn't seem to have spread to Europe in the Middle Ages or the Renaissance, at least not in large numbers; and far from being small weapons restricted to assassination or small-game hunting, the Chinese crossbows shown in the articles linked above are predominantly large enough to carry bows of sufficient power to make them into practical military and/or general-purpose crossbows.