bcoulan, when a module says it can do something, but you are simply having trouble getting it to do what it says it can do, you don't post under the "request" forum asking for help getting the said feature to work. :)
That said, when you have this sort of issue where you are simply not understanding what the documentation says, you should jump on IRC (irc.freenode.net) #litestep and ask for some one to explain and help out. It is hard to respond in detail in a forum post when there isn't much more to say, than what the documentation already says. It would be much easier to walk you through it.
But if you still want to try it on your own. Re-read the documentation a little bit closer, and use this util to find the window class it is talking about: http://www.shellfront.org/utils/winspy.exe
That is about as clear as we can get without stepping you through the process. Good luck! Please join IRC if you need further help on this.