Ah! Just checked on Eurail and found out that there's no such thing as One Country Pass for France! What a bummer seeing that I'm only traveling in France in this coming spring/summer!
So don't ask Eurail. Rail Europe offer such a pass, which you can buy from there Singapore based operation, which is the closest they have to Malaysia. Admittedly, though, RailEurope tend to add large mark-ups and aren't usually anywhere near the cheapest option.
Also, I know it includes Benelux that is of no interest to you, but especially if you are going to make a few long trips, the France-Benelux pass may work out cheaper for you. Obviously the cheapest pre-booked SNCF tickets are cheapest, but you have to pick your exact journeys/trains 2-3months in advance to get them. For more flexibility, the pass might work out better.
Note that even with a pass, all TGVs, Corail Lunea long distance and all night trains require compulsary resvervation that you will have to get/pay for separately and their are only a limited number available for each train.
Finally, for more general info the Francerailpass site gives you more info and details on where to buy and what they do.
[ Edit: Edited on Jan 12, 2009, at 8:42 AM by Gelli ]