First, you've posted in the Mac Pro desktop forum. Do you have a Mac Pro? (There's a picture of it at the top of the forum.) Some Macs have optical (DVD) drives and some don't, that's why it's important that we know what kind of Mac you have.
If your wedding DVD is a regular DVD that you can play on any computer or DVD player, you'll need to "rip" it onto your computer. Use Handbrake for this - it will create a video in MPEG4/H.264 format. I'm not sure what you plan to do with it from that point, but H.264 is pretty universal.
I'll point out that one can also make a disc image of a non-copyprotected DVD, from which one can play like a normal DVD on the Mac, or make exact copies, all with Disc Utility. At least, up through OS10.6 (dunno about after).
AFAIK, if you use Handbrake to get the raw video, you would have to reauthor a subsequent DVD.
Put DVD in drive.
Hold down alt (or option) key and drag the DVD icon on your desktop to an empty space on your desktop. It will make a copy.
Eject the DVD, leaving the copied folder with the same name as the DVD on your desktop.
To play it:
Open that copied folder. Drag the VIDEO_TS folder you will find inside it onto DVD Player, and it will play your copy of your DVD from your HD.