Editors note:
There seems to be great deal of confusion about playing DVD's
especially using Windows Media Player. WMP can indeed
play DVD's..however..a DVD drive and "Codec" must be
installed on the computer.
The discussion below should help clarify the issue.

Thanx to "PoohBear" for submitting this article. :)

To play a DVD with your computer you need 3 things.
First, you need a computer with enough "oomph" to play DVD video.
This includes plenty of RAM and a fast processor.
I have seen it done on systems with 256 megs of RAM
and a 600 MHz processor, but that was all it would do.
No multi-tasking.
Better would be 512 megs of RAM or better, and at least
a 1Ghz processor.

Second, you need a DVD drive. You would be surprised at how many
people try to play a DVD using a CD player.
The lasers are different and they are not compatible.

Third, you need software to play the DVD.
You can play a DVD using Windows Media Player,
but you will have to download and install a DVD codec.

A codec is software for COmpressing/DECompressing video files.
Different codec's process different types of files.
To play DivX files you need the DivX codec.
To play DVD files you need the DVD codec.

Your DVD drive probably came with software..(codec)..and it's own
"media player" for playing DVD's.
It is likely compatible with Microsoft Media Player,
so you can use either player as you wish.

Note: When you install a DVD drive..or a DVD codec..you may
find that it sets it's own 'media player' as the default player.
Therefore, when you insert a DVD disc, an unfamiliar media player
may appear. This may be the best overall choice..however..
if you prefer Windows Media Player, you can set the options
in both players to make WMP the default player.

"Third Party" software (other than what came with your DVD drive)
is available.
Two examples are PowerDVD and WinDVD, but there are others
available for playing DVD.
Remember, Windows Media Player will only play a DVD
if a compatible Codec is installed.

If you have a computer that is powerful enough to play a DVD
and you have a DVD drive that you know is working
and you have the software installed but you still can't view DVD,
make sure you have the proper codec.
Microsoft has codecs available for purchase.