In reply to Sonya Mc: Trips on India's train network can be booked online. When I was last there (January 2011), foreign travellers had to book through Cleartrip.com (small booking fee, a few pence I think) if they wanted to use the online service. Found it pretty useful myself. You can get on waiting lists for tickets, often you can be 140-odd people down te list but still get a ticket - trains are very well patronised so cancellation of tickets by those who no longer want to travel is the norm.
The route I took was from Chhatrapati Shivaji Terminus railway station, which is the nearest station to the backpacker hangouts in Mumbai. Confusingly, auto rickshaw & taxi drivers will call this VT (the station was known as Victoria Terminus), just as many Indians still call the city Bombay. From memory I went from Mumbai to Hubli on a sleeper, took around 20 hours or so (short in Indian terms), changed trains after a few hours wait to get to Hospet, then hopped in a rickshaw to Hampi. All in all, i think the journey took 30 hours. The bouldering is mostly (though not exclusively) in the old village the other side of the river, crossing closes during the evening.
I found this website pretty invaluable when trying to get my head around Indian trains:
http://www.seat61.com/India.htm As a precious poster commented, second class sleeper is great (not so much the air con carriages). I always seemed to be fed home cooked food by travelling Indian families who wanted to know what I made of it all - invariably it was amazing & a great experience.
Hope this helps & I'm sure they'll have a cracking time.