What file format does Windows Media Center use for Recording?

“What type of file format does Windows Media Center use to record television?”
Windows Media Center uses the DVR-MS file format, which is an ASF container with MPEG-2 video and AC-3 audio packaged in a slightly non-standard way. ASF is the same container format used for Microsoft’s WMV video files, with the difference being that WMV typically uses WMV video and WMA audio. The files aren’t recognized by many other media players and video conversion software frequently fails to convert the files to new formats because it’s unrecognized.

If you want to burn your DVR-MS files to DVD, MyDVD is probably your best option. Here’s a tutorial on how to burn DVR-MS to DVD.
A couple of reliable solutions for converting DVR-MS files for playback on an iPod are AVS Video Tools and Digital Media Converter.