PWM is " Pulse Width Module" just Google it

Yeah sorry , that's what i mean :)

Arduino will be the best solution for you. The link below will lead to the arducopter project which is based on open hardware category.

http://code.google.com/p/arducopter/

Thank you very much , really useful

U can use ARM controller with Rtos support 

try raspberry Pi

try stm32f4, you can design pcb for it by yourself , it can be tiny and light, of couse it's also easy to learn, enjoy it!

Thank you i'm gonna try it very soon.