Well, there's a couple ways you could do it:
With minimal editing: Womble MPEG VCR can edit the .vob (dvd) files directly, once they are ripped to your hard drive. You could then create menus and author it with Nero.
For free: Demux the .vobs with VobEdit, edit with Cuttermaran, and author with DVDauthorgui. Demux means split the DVD file into separate video and audio streams (a .vob is the 2 combined).
Or you could get a software editing/authoring program like something from Ulead, Pinnacle, etc... then you would demux the .vobs and do everything else in that program.
There's a lot of ways to go about doing this, but the basic steps are going to be the same regardless of what you use to do it.
You should be able to find all the programs I mentioned above through Google...