Thanks - I figured that the easiest way to convert files would be through quicktime pro.
Also, I found out that half of the time, the slideshows in iPhoto I send to iDVD become narrower and look distorted when I move them to iMovie - I checked the info of the files, and found out the ones that don't get distorted are the ones with the Codecs listed as "MPEG-4 Video, Apple Lossless, Tween". The ones that do get distorted are MPEG-4 Video only.
I'm guessing I'm not converting them the most efficient way (Share>Send to iDVD, and then finding the new file in my Movie folder), but is there a way to control the way the file is formatted? Or is there a better way to get the best quality movie files from iPhoto slideshows?