converting files and burning to dvd

hi since im new i thought i would ask for help just downloaded a couple of movies and was getting ready to burn wehn i tried to add files to my nero it said they couldnt be added i have nero 6.6 and normally i just add video files click burn and they burn, one file is an avi the other says dvdrip.ac3 any help would be appreciated thanks

sorry but you posted this thread in the wrong type of forum.