I seem to be on a roll this week of converting file formats. I received a vob file from a client, which I needed to convert to mp3 for transcription. It proved really easy using Audacity which you can download free here http://audacity.sourceforge.net/.
Like everything, unless I use a program regularly I do forget how it works and I usually need to do conversions quickly so haven't got time to learn how to use new programs etc. However I find Audacity really easy to use.
So here's how to do it:
File > open your vob
File > 'export as mp3'
Then give Audacity a few minutes to do its thing.
Of course Audacity can be used for much more than just converting formats. I also used it to split the converted mp3 into separate files using the Trim facility. I just highlighted the part in the audio that I needed as a separate file and clicked Edit > Trim and saved the file under a new name.
What do you use to convert file formats? If you know of any programs that are really easy to use I would be very interested to hear about them.