I'm assuming you're working with a video editor. Is this right? If so, ask him to export the video from the NLE to 25 fps. But then, ask yourself: are you going to do a layback to the NLE after exporting the audio? If so, you've got a frame rate mismatch and a big problem. Or, are you going to export a video directly from Pro Tools (as an MOV file, with embedded audio mix). If it's the second, there's no problem.
If you're NOT working with a video editor and this is just a video you picked up somewhere that you want to, say, do some sound design for, then you should convert the video to 25 fps before importing to Pro Tools. If it's an MOV, use QuickTime Pro, FCP, Avid or whatever to do a conversion. (I'm confused because first you said it's an AVI then you said it's an MOV.) The video quality might get wonky. It depends on how large the file is and what the existing video settings are. If it's small or massively compressed, the conversion will make it worse.