Issues to burn multiple VCD on a DVD

Tried to merge a set of VCD movies on a DVD and got some trouble as the following:
a) TMPGEnc DVD Authoring
It was successfully merged about 7 VCDs (with total about 4.3G mpeg1 file size) on to one DVD. However, the DVD can only be played by computer not by any of the DVD players. Does anyone have the experiences on this to share?
b) NeroVision Express 3 SE.
Whenever a .DAT or .mpg file was added to the software, it shows up much larger size than its original file size (about double the size). Therefore, it ends up only about 2G of the .DAT or .mpg files merged into a final DVD. Tried to adjust the DVD options as 352x240, it doesn’t change the size at all. Any thoughts to share?