The videos that you download with Limewire will almost always say if they are AC3 in the filename. And in most cases that will be 5.1 sound. If it says nothing then it is probably 2 channel. This should not have such a large inpact on your finished DVD as Nero should just convert to 2 channel if you chose that. Not sure how the other way around will work. I will probably just copy the channels on to other channels not giving much effect.

Must admit I usually have it set on automatic as well and 1 pass for a video thats around 1400 MB or two pass for videos that are around 700 MB.

Also I haven't used Nero 6 for a while now. Nero 7 has Nero Express and one program and Nero Vison as another (off course using Nero Express for the burn process)

One thing you might look into is if your setting may say PAL or NTSC format. Nero converts it to same format as source, but you can tell it otherwise.

Also interlaced is the normal way to convert to DVD. Even commersially I believe.

If Windows Media Player plays it fine then Nero should be able to use the same codec as WMP did

If you still have problems getting it to work then I would suggest you try the SUPER converter that WW recommended. Just make it to DVD and the use Nero Vision Express to burn it.