I just find a free video to iphone converter for mac, it's likely free only for a month, sounds like a good application for we iphone owners, since it can support iphone 3g and the newest iphone 3gs.
I have already downloaded it, very easy to use, just google search Wondershare video to iphone converter for mac and go to the website to get the freeware.
I know handbrake, but as a beginner, i think it's too professional, so this freeware is my first choice since it's very easy to use with the same function to convert videos files for iphone.