C:\Users\Public\Recorded TV. Set recording options in Windows Media Center
The files are recorded in .wtv format and can be converted to .dvr-ms format. Convert a recorded TV file (.wtv) to an older format
Shows recorded in HD are large and have to be transcoded to fit on a DVD, whereas files recorded in SD, have to transcoded also, but are easier to fit onto a DVD, because of smaller recording qualities.
HD uses a fixed recording quality.
SD....you can select a different recording quality (Fair, Good, Better, or Best). Managing recorded TV shows in Windows Media Center: frequently asked questions
My point is, that if you plan on burning files to DVD, it's easier to record in SD and work with the smaller files.