If the wmv's are encrypted then it's going to be really hard. If not you can follow this guide (
http://www.dvd-guides.com/content/view/58/59/) and it'll guide you through the steps. Notice it's only a trial (WinAVI). You can find more tools to do it at
http://www.videohelp.com, but WinAVI is one of the easiest methods of converting non-encrypted WMV's.