The hard part is to copy a DVD to hard disk in the first place.
Because DVDs are copy-protected these days. You may google for "ripit4me" to find the whole story about what people do to copy DVDs and how industry tries to prevent it. I hope this is hint enough
To do the same is legal in some countries and illegal in others.
Once you have a backup of your dvd on hard disk, you may use "Nero Recode", part of "nero8", to convert to MP4/AVC aka H.264. It is known to be the best tool for it.
Nero – leading digital media solutions for consumers and professionals - Official website .