You say you have an American TV, and if so, your French console will probably not display properly on it. But if you want to try it anyway:

http://www.beststuff.co.uk/slx_rf_modulator.htm

If the O3 uses RGB for it's SCART cable, this will probably convert it to a PAL format RF transmission. If the O3 uses composite, it may not work at all (France is a SECAM country).

What you need here is documentation, and lots of it. And format convertors. If you just want to connect it to your TV check out:

http://www.diyha.co.uk/electronics/scart.html

You want to wire pins 17 and 19 to video, and 1 or 3 and 4 for audio.