The answer very much depends on what you want to do with the vob files? Heres a few suggestions.
1) I've several vob files that i've backed up from a DVD, but I forgot to backup any of the IFO files! Remember that vob files contain the actual video, audio, and subtitle streams but the IFO files contain the chapter data etc.
My vob files are about 7gb and I aim shrink these to 4.3gb then back them up to a standard dvd+r. I use DVD shrink but this will only accept VOBs if the associated IFO file is available, hence we must first recreate an IFO file. To do this use a freeware program called "IFOEdit", do a search on Google and you'll find the download. Within IFO edit there's a button around the bottom middle that says "Create IFOs" click this then select your VOBs and select the destination directory as the same as source.
No open up DVD Shrink and all should work as usual, remember that the chapter and menu data will be lost so your end DVD will be a single track.
2) If you want to extract the video and audio data to say a MPEG2 file for editing then this is a little more involved but the following should work: You'll need VobEdit and TMPGENC (Free version within the first 30 day trial period) both can be downloaded for free. If TMPGENC has expired you'll need to buy TMPGENC plus or TMPGEnc Express, I've been unable to find an alternative.
First open up VobEdit and on the bottom button bar select open, find your first VOB file within the collection and click open. Next click on the "Demux" button, check the "demux all video streams" and the demux all audio streams". Click OK and select the output directory, click save and wait.
You should now have at least 2 files depending on how many video and audio streams were within your vob files. One of the files ends with .m2v and the other with .ac3 the first is the video stream and the second the audio. If you've multiple of each then I'll let you figure out how to determine which streams your after.
Now we need to mux these 2 files into a single MPEG file. Open up your choosen version of TMPGENC and on the file menu select "MPEG Tools". Select the simple "Multiplex" tab, on the drop down box select M-PEG2 VBR, then in the next 2 boxes select your video and audio input streams finally determine where your output file is to be located and click the start button.
You should now have your MPEG file. I'd now use a program such as TMPGENC DVD Author to burn this back to a DVD as you have control over chapter positions etc.
Hope this helps,
UKSamo