If you bought the drive from a store, it should have its own drivers and codecs with it (usually).
Either way, while WMP is okay, I would suggest buying a DVD program if you watch a lot of DVDs. Personally, I use WinDVD Gold.
You'll just have to try it out. If you can get WMP to play your DVDs, and you like the response you get, then fine. If not, I'd go buy something (like WinDVD). It's a matter of preference.