You can find more information and resources at the Timex Data Link USB web page. Note that I have been having problems with this first link. As an alternative, you could try the Canadian Timex Data Link USB site.
You run a program under Windows (screenshot below) to define what modes (applications) and configuration settings you want installed on the watch, then connect the watch to your computer with the supplied cable. Settings are sent down to the watch while data (such as saved split times from the chronograph) are uploaded to the computer.
There is a excellent Yahoo Group: Timex Data Link USB Development (timexdatalinkusbdevelop) where you can find many WristApps available for download, as well as a Watch Emulator/Debugger, in case you want to try developing some WristApps yourself (or just test drive some before possibly downloading them to your watch). You will want to join this developer group to get access to the available downloads. If you want to talk about the watch as an owner/user, then you should take a look at the Timex Data Link USB (timexdatalinkusb) Yahoo Group.