|If the DVD has copyright protection on it, you cannot copy it legally.|
however, if the DVD does not have copy right protection you can make a copy with Nero Express. Please refer to the user documentation for your version of Nero Express.
As above, DVD's come in both single layer format and dual layer format. If you original DVD is a single layer DVD (should be about 4.5gb in size - right click on your DVD drive in 'my computer' and chose properties to find out the size) then Nero will let you copy it to a single layer blank DVD. If however, the original is a dual layer DVD (around 9gb in size), you will either have to copy it to a blank dual layer DVD or Nero may let you "shrink" the original DVD so it will fit into a blank single layer disc.
Make sure you buy the correct TYPE of blank DVD disc.
Have a good read about the afterdawn.com/guides website jboy recomended.