You can use lossless DRM removal tools:
FairUse4WM or
drmdbg +
freeme2/drm2wmv.
If it is too hard for you to use lossless
DRM removal software, or you can't set up your system to use them, you can use the following lossy DRM removal tools:
Soundtaxi,
MuvAudio,
Tunebite,
freeTunes,
Note Burner.