Ogg and FLAC are two popular formats that are being used more and more. If you like WMP but need to listen to this file type, then you just need to convert the files or install the codecs.
Ogg is an mp3-like compression audio format except that it is open-source and patent free. Many audio users like this format over mp3s; however, WMP doesn't play these files by default.
FLAC is a lossless audio format. This means that the audio is compressed (not as much as mp3 or ogg) but there is no loss in quality. WMP doesn't play these files by default either.
To get WMP to work you have two options...
1. Install the codecs
You can download and install the codecs from here:
http://www.illiminable.com/ogg/
This should allow you to open either of these two formats in WMP just as you would any other audio formats. As ogg and FLAC formats have changed, however, you may not be able to play every file.
2. Convert the formats
Encoders like dBpowerAMP can convert ogg and FLAC files to more well known formats like mp3 or wma. Just remember by converting to these file types, you lose the advantages of the other file types.