having been educated in the realm of computer science, i used the binary number approach (just make sure you have enough serpent coins):say there are 4 switches (i can't remember how many there are right now), like so, and they are all facing down:
0 - 0 - 0 - 0
throw a coin in the slot, and see if a door opens. if it does, get the treasure. either way, continue flipping switches like so until all doors open:
0 - 0 - 0 - 1
as above, throw the right-most switch. throw another coin in the slot, etc. etc. the next few switch positions should be like so:
0 - 0 - 1 - 0
0 - 0 - 1 - 1
0 - 1 - 0 - 0
0 - 1 - 0 - 1
0 - 1 - 1 - 0
0 - 1 - 1 - 1
if you try every possibility, you will need 16 serpent coins. but, for me, i remember it taking only a few...
anyway, take this for what it's worth - and good luck!
jason