Indian Railway

3 months ahead. Right now you can book early November. And it will depend on the train and the timing whether booking ahead will help. During Diwali (Diwali 2010 : Friday, November 5) you want to have seats on most trains, don't bother with waiting list, it's likely not going to happen.

It's the largest railway in the world, and the 2nd largest employer in the world. I am not sure there is a comparison. In spite of itself, it works well.

Depends on if you are capable of keeping an eye on things when you're sleeping, securely locked, etc. Otherwise, as someone I traveled with once said, "There's a better class of people in 2AC".

Like pirate said, booking opens 3 months ahead. Since you're traveling in Nov - Dec, I would recommend booking ahead as much as possible. Diwali is holiday time across the country, and mid-late December is when schools have winter (ahem!) holidays, so thats also a time when its difficult to book tickets. If you know your itinerary, its best to book ahead rather than arrive there and hope for tickets.

If this is your first time in India, and you're a little bothered, maybe you could start by traveling in 3AC for your 1st journey, and then do non-AC sleeper for your next journey. Also depends on the length of your journey - if its longer than an overnight journey, definitely book AC. In non-AC sleeper, be prepared to be met with loud (and often intrusive and curious) co-passengers, strong smells (whether of packed food, or the loos), lots of vendors and some beggars, dust and grime. These are there in AC sleepers too.....only, to a lesser extent.

Oh,the fun of travelling by train!

Personally, I think regular sleeper class is fine as long as it's not crazy hot out, which it shouldn't be in Nov/Dec. Yes, lock your bag - Indians do it, so it's not like you'll be appearing to be a paranoid westerner. More crucially, try to get a upper berth if you can (the lower ones double as seats during waking hours, while the upper bunk always remains a bed, so you always have the option of lying down if you want it). I'd say look at your budget, look at the train schedules, and make your choice based on that. There's really nothing wrong with regular sleeper.

Ditto Oobski! One time I went AC in the summer. It was sort of air conditioned when moving without openable windows..