If you are using DVDFlick, you are converting avi files to dvd-video, which does take some time, depending primarily on the speed of your cpu. If you are converting from files on the optical drive this will slow down the process unnecessarily.
The best way to process avi to dvd-video is to use two separate hard drives. Have the original avi file on one, then have DVDFlick output to the second one. Once finished, you burn to an optical disk if you want a hard copy. If this is not possible (say you only have 1 hdd), then do all of the conversion on that hard drive...but don't involve the optical drive until the last step, which is the actual burn to the disk.