1. To burn an ISO image with Nero: Nero Burning ROM > Recorder > Burn Image... > select image, etc. This is in Nero 7.x. I think it is the same in 6.x.
2. The option does not appear in Nero 7. Just burn with the default setting.
For Nero 6:
Open Burning Rom
Select "DVD-Video" icon on the left side.
Click "New".
Click "Recorder".
Click "Burn Image...."
Or...
Open StartSmart
Make sure you are in DVD mode, at the top.
Click the "Copy and Backup" icon.
Click "Burn image to disc".
I have no idea where you found the "Disc at once" setting but set it to 'Disc at once". I took a look at my Nero 6 and could not find it. Where is it located?
I use CD mode, not DVD.
I am not on Nero PC right now, but as I remember, Nero Burning ROM > Recorder > Burn Image... > select image, OK, this open burn window, on tabs called 'Burn' is few settings, from right side is drop down selector, by default it stay on 'Track-at-once', to burn .ISO, its necessary select 'Disk-at-once'.
1. I think the procedures to burn an ISO image to CD or DVD are the same. Just select the drive unit (NBR > Recorder > Choose recorder...) and insert the right disc on it. Then Recorder > Burn image...
2. ImgBurn is small, freeware and may be reliable. But it is not easier to use than Nero. Just look at the Tools > Settings window. Lots of options in 10 tabs. It is "simple" if you use the default options - but the same is true of Nero.