I've just added a PDF download into the Member Centre that contains detailed timetable and fare information for the main trains within the Vietnam rail network. The three page document includes:
SE1-6 Hanoi - Saigon - Hanoi
TN1-4 Hanoi - Saigon - Hanoi
NA1-2 Hanoi - Vinh - Hanoi
TH1-2 Hanoi - Thanh Hoa - Hanoi
LC1-4, SP1-4 Hanoi - Lao Cai - Hanoi
DD3-4 Hanoi - Dong Dang - Hanoi
HP1-2 LP5-6 Hanoi - Hai Phong - Hanoi
It also includes fare information (in VND).
All the information was garnered from the Vietnam Railways website on September 15, 2007, so it's as accurate as their website. It doesn't include every single train in the country (for that you can use the Vietnam railways website yourself!) but it does include the main trains that most readers may be considering catching.
It's free for all Travelfish members, available for download in the Member Centre.
Hope it helps your trip planning!