If you can purchase them online, it would probably only work in big cities. It may bec convenient for some, but I'm not ok with putting my passport info into just any database. It may be new, but that doesn't mean it's better. Also, I think I read an article on Echinacities that said to make sure you rip up your ticket after you're done using it, because people can scan it and unscramble the info. Just a friendly warning. Have a nice day.

http://www.tieyou.com/ does online ordering and you CAN fill in passport number. It is in chinese but you can google translate it.

And on this link you can find all train schedules.
 http://www.cnvol.com/
You also can let train tickets deliver to your door with paying a extra of 5rmb.

For 15 years almost I have traveled within China by train, and never was asked to show my passport to buy a ticket, or to enter the train station or board the train.  Once inside the train, the conductor will come around asking Chinese persons for their ID cards and writing out on a sheet name and numbers of all passengers.  In my case, I do ask conductor for the sheet and pencil and write out my name and passport number.  They all thank me for my help, maybe because could not understand one word of what the passport says, and end up with a name like United States of America, and my passport number will be my date of birth.

Try http://www.mangocity.com/

The ONLY official website is www.12306.cn

Foreigner can also use it, but there is NO English interface.

I tried it and it worked out, after you pay online you can just go to get your tickets at the counter at the railwaystation (just before you leave)...