You can also use MPEG Streamclip to convert it something native, depending on the resolution and frame rate of the .avi file.
Also .avi is a container for codecs like DIVX/XVID and so on, like .mov is a container for .h264 and Sorensen codecs and so on.
So the file type matters, but the codec matters a lot more.
Btw, if the .avi is in SD quality, you could use the Apple DV codec, when you convert it vi MPEG Streamclip, which is way faster than QTPro in my experience.