Womble mpeg video wizard seems to be the favourite program on this forum for those editing DVD files. However, if all you want to do is an exact copy of the 8cm DVD to a full sized disc then there is no need for any editing programs. Just use Nero (or whatever burning program you have) and do a straight disc copy.
If you want to just combine the contents of a couple of discs onto one then you can rename the .VOB files to .MPG as already suggested and then use Nero etc to copy the multiple files onto a single disc.
If you do want to edit out the boring bits (the majority of it in my case

) then you do really want to look at buying Womble mpeg video wizard etc as this should give far better results than most of the standard editing programs as it is specifically designed for editing MPEG video, where most are designed for .AVI editing.
Mark.