Older computers used to come with dvd drives that either took one type or the other but nowadays they take either so If you have a computer with xp,vista or windows 7 then it most likely you don't need to worrie what type you get
Sorry for the mistake in the previous post If you burn say a video to a DVD+R then it wont play on your home DVD player as it doesn't support it but you will be able to view it on your DVD drive in your computer . The two formats are completely different and cannot be converted. Always use DVD-R as it the one that will play on yout home VVD player.