A dvd is made up of many files, inside a Video_TS folder.
One of these files is the .vob file.
A .vob file is a wrapper that contains one or more mpeg2 files in a format that a dvd player can read.
When you author a dvd you take your initial file, which may be something like a dv.avi file. This has to be converted to an Mpeg2 file.
From here, you make the vob file and then burn your dvd.
The vob file, as mentioned can be made of one or several mpeg2 files. It is a maximum of 1gb in size.
If you have a 1gb mpeg2 file then this will be made into a single vob file.
If you have four 250mb, they will become a single vob file.
If you have a 4gb mpeg2 file, then it will become four vob files.
Some people say to rename the vob file to mpeg2 to work on it. This can fail, as when you rename it to mpeg2 the majority of times only the first vob file will show up. So taking the above examples, number one would show up correctly, but number two would give you one 250mb mpeg2 file and you'd lose the rest in cyberspace!
Some dvd camcorders will make hundreds of mpeg files each time you stop and start recording, so imagine how much you'd lose by using the renaming scenario.
The easiest way to handle these files is to convert them to something that can quite easily be used, such as wmv for movie maker.
You will lose a small amount of quality when you do this, as you are converting from one compressed file format to another, but converting to any other file format will result in a similar quality loss and it's something you have to decide on - is it worth it to do the editing I want. In most circumstances, you probably won't notice the difference!!
See this page for more help with converting vob files.