I'm new to Macs so please forgive my stupidity. Someone gave me a movie or video file with the extention .avi. It won't play on my iMac. Someone told me I need to buy Quicktime Pro for 30 buckaroonies in order to play such files. I just got a Video ipod so I want to try watching a movie on it. Do I need to buy some additional software? My iMac has just the basics.