Cheers RafkeP, I finally found what went wrong thanks to your help. 8)
I installed Girder and followed your instructions. The green circle was flashing to yellow when pressing the usual keys, but not the additional keys (play, pause, etc).
Then I searched the Girder forums for topics speaking about Logitech keyboard. Someone there says that the Logitech keyboard driver is preventing the keyboard to work with Girder.
The logitech Keyboard driver is called "Itouch". So I closed the Itouch program from the systray, then tested the Girder green circle with the additional keys. BINGO! It flashed yellow.
Then, I wanted to check if it was the same situation in Bsplayer. I went to Bsplayer's settings, pressed the "pause" key of my keyboard over the text box, and BINGO again, the text box showed "#179". Then I tried to pause the playing movie with this "pause" key, and it worked like a charm.
Unfortunately, I tried to restart the Itouch program, then pressed pause in Bsplayer, and it didn't work anymore :(
So I don't know how to make Itouch and Bsplayer co-exist. perhaps I could make a script that would shut down Itouch, then launch Bsplayer, and another script that could shut down bsplayer then lauch Itouch, but it wouldn't be the best thing to do. The other way would be to buy an infrared port and a remote
Or if anyone has ideas, let me know, thanks.