Assuming friction shifting:
Can you run a 9 speed chain and front derailleur on a new Shimano 10 speed MTB double or triple?
or is the 10 speed derailleur required? If so, will the 9 speed chain work?
I am currently using a 9 speed chain with a Sram XO 10 speed double crankset and an 9 speed front derailleur and it works fine.