I would disable iphoto asking to import for starters, it will be a headache later. I am almost sure imovie will import and convert your files for you, either Flipcam or GoPro. That might be you best route. Another idea is to get a small external hard drive and store all your video files on that, which is more idea to be editing any video format. Make sure to get a drive that is 7200rpm, most laptops come with a 5200rpm. 7200rpm is more ideal for video.
On another note, keeping your media completely separate from imovie might be ideal and just import it separately so when you do upgrade to FCE it will be a better transition, instead of digging throu imovie folders.
hope that helps