It's keeping them as .avi files and want to play in Windows Media Player. I'm not getting the option to change the file to an .iso (if I need to, I'm not sure). I'm still lost here.
You do not need to make an ISO. Extract the video file, your AVI,and that is what you use with DVD Flick to convert to DVD, or with NeroVision. Unless you have a Divx certified player. If you have a Divx player, no need for conversion, just burn as a data disc.
Well, if the video needs subtitles, then DVD Flick, as adding subs with Nero is a pain in the arse.
Some people report out of sync audio/video with Nero. I have seen some sync issues with DVD Flick too though. Both output good quality( I can't say one is better than the other regarding the quality). On my machine, when both are set for high quality encoding, 2-pass, DVD Flick is faster. The menu creation, has more fancy options in Nero, but that might be the cause Nero Vision was slower.
You get subtitles if using Nero Recode for example to reauthor a DVD, or recode to mp4, but not external subtitles when using NeroVision to convert AVI for example to DVD, with embedded subtitles. Not with Nero's original codecs anyway, you have to disable them and use FFDShow instead.