One of the easiest ways could be you to boot your pc using a live Linux distribtion CD/DVD that allows you to mount the CDfs file sys (to do that you need to have 2 drives in your machine as one will be locked by the Linux distribution) and to extract the avi files to the HDD.
If you get that you will be able to copy the files (or the image) under windows to a UDF file system, as your problem is not a file system convertion but the copy of the files (or image).