It may be easier for you if you look on this site.

http://www.seat61.com

Good Luck.

Ian

Thanks for that info Ian.

Depends when you want to go but it is not like UK - just turn up and pay at the station and get on the train. We have just been up to Mumbai and booked it in December. These trains are full and have waiting lists and if you do not book far enough in advance you have to go on a waiting list - you move up when they have cancellations (bookings taken 90 days prior to travel)
You can book on line but have no idea how to do it as we are in Goa and go to Thivim station a couple of months before we want to go and book and pay. Thivim is about 15 mins taxi ride the other side of Mapusa and cost 350 rps.
As to your other questions - we leave Thivim at about 3.15pm and arrive in Mumbai about 11.30 - this is the express train - there are other trains which are slower and we have also been on the overnight one which leaves Thivim about 6.30 in the evening and gets into Mumbai about 7.30 in the morning but not - in our opinion - a very comfortable sleep - did it once and never again.
Lots of food and drink on the train - always available - water from 12-17rps depending on the train - chai - coffee - tomato soup - soft drinks - the boy comes up and down the train all the time. The train staff come with sandwiches, snacks, fruit etc and at some stations people come on the train and sell fruit and snacks (have the potato cakes with bread rolls - wonderful). You can also order a full meal which they bring at a set time (late lunch or dinner depending on the train time)
Not like British Rail as in captives and have to pay loads of money for food - we love the Mumbai/Goa train and would choose it over flying when we have lots of time but not the best if you are on limited time - i.e one day up and one day back plus time in Mumbai.
Don't miss Mumbai - it is a wonderful place - much prefer it to Goa but then that is me.

I do know that there are seats which are not sold via pre-paid tickets which are reserved for various sections of people like emergencies/old people/tourists etc and rang a Goan friend to ask him if it was possible to get any of these tickets at short notice and he told me - yes anything is possible if your pay the agent and he said to go into a travel agent where you are staying and ask.