My advice - don't even bother with WiMP. It is by far and away one of the worst applications on the Mac and that is not being extremist.
Your alternatives are to get VLC or Mplayer (both free and both worth having anyway but they don't play all WMV) or pay $9 for the Flip4Mac WMV player which will let you use Quicktime to view non-DRMed WMV files and works extremely well 98% of the time.
Search versiontracker.com or macupdate.com for them.