I'm just wondering, what is the difference between the Duemilanove and the Mega? The reason for my question is; i would like to run a stepper motor i have at a higher RPM than 80 wich i can reach with the Mega. I notice a significant difference in price between the Duemilanove and the Mega, although the Mega has more ins/outs and more memory. Because i am very new into the world of electronics i can only imagine that this price difference lays in the speed in wich the Duemilanove processes the program. I know they have have different Atmel chips but have the same clock speed of 16MHz.
Can somebody help me?
You pretty much nailed it - different processor, different # of IO, different amount of memory.
Other than that, the same. Both have the same 8-bit core running at 16 MHz so you won't see any difference in processing time.
Same for any of the 328P based boards. If its just 1 motor and some IO and you don't need USB in your final project, perhaps a Promini is all you need. Use an USB/Serial module like FTDI Basic to program it, or your Mega even (Ground the Reset pin on the Mega, connect Tx to Tx, Rx to Rx, Gnd to Gnd, 5V to 5V, start the IDE download, press Reset on the ProMini when the IDE shows "compiled xxx of 32xxx bytes" )