Read some guide contained in http://www.afterdawn.com/guides/, for instance http://www.afterdawn.com/guides/archive/convert_avi_to_dvd.cfm (but you need an application which manipulates mpeg-2 input, like TMPGenc Plus). Just avoid the codec part, since you don't need a codec for decoding mpeg-2 files. I don't know how 'good' are those MPEG-2 files; just take care that garbage in = garbage out, so you must decide to encode a SVCD movie into DVD (wrong) or to encode multiple SVCDs into a DVD (good).