Subject: Buying French Train Tickets on Line

In looking at the French Train site - - they list ticket prices much lower than buying from Rail Europe (a US site). In addition, they have discounts if one purchases a ticket 7 or 30 days in advance. However, they appear to not allow purchases or reservations to residents of Canada or the United States. Does anyone have information about using this site or purchasing tickets on-line directly from SNCF?