Finding Nemo is a 4:3 full screen movie (most kids cartoons/animation are) so will play full screen regardless what format its in.
Fast & Furious is a 16:9 widescreen and ifyour DVD plays it fullscreen then you have your DVD Player set to do that, it just chopping off the left and right sides. This is called Pan & Scan.
You have a couple of options, either 1.5x zoom the VCD playback and it will then be full screen (left & right sides cut off) but of lower quality or use another program to do the conversion. Have a read of the 2 DVD to VCD Tutorials (Tutorial section), both can allow you to make a 4:3 from a 16:9 and both use TMPGenc.