Welcome to the forums.
It sounds like you are converting video files (of unknown type) to dvd-video. Though we are in the dark a bit on what types you are starting with, I normally suggest one particular conversion program for this process, since it has proved reliable and can output in very high quality. That program is called AVStoDVD, and is free to download and use. You can find it here: http://www.videohelp.com/tools/AVStoDVD
AVStoDVD can be set up to burn automatically with an excellent burning program called ImgBurn. ImgBurn is also free and included in the download package. You can also install it separately…I recommend this, since you can go in and set the burning speed to less than maximum before you start your encoding process with AVStoDVD. Set it to 8x or 12x, and ImgBurn will remember that speed setting until you change it. You can download ImgBurn here: www.imgburn.com It will coexist with Nero with no conflicts.