You can't actually Capture, or at least should not, as capture is a term generally referred to when you are capturing a tv broadcast, capturing vhs to dvd, or transferring from a video camera to pc.
You can copy, edit, and re-encode the files on your dvd's. If you just want to copy them, you can do that with no quality loss. If you want to edit the vob files, and add menu's, you will have a very slight quality loss. If you want to demux the vobs back into avi files so you can do frame accurate editing, and run filters against them to clean them up, you will have some quality loss, depending on what processes you use.
So, everything pretty much depends on the specifics of exactly what you want to accomplish, and why.