It is probably better to start a new thread with a title like "Crank Arm Length Question" but really there are already such threads such as :
http://www.bikeforums.net/showthread...rankarm+length

You could read through these and if you have more questions append your question to the appropriate thread.

If you have questions about gearing there is a sticky about gearing here:
http://www.bikeforums.net/showthread...imer-for-Newbs