Hi! I plan to take the train (one way) from Bangkok to Chiang Mai since quite a few people suggested here that the scenic ride is worth seeing. Can anyone help as to how to book and which classs etc. And what is the quality of Thai Trains?

Website run by a train aficionado. Includes pics of various class cars.

http://www.seat61.com/Thailand.htm

Why not just look into when you're in Bangkok? You may find out what you need or even decide it's cheaper/easier to take a bus.

There's also Lonely Planet, etc. for general information.

or u could skip the incredibly long journey and just fly,its v cheap with air asia