Try AviSynth.
See this post I did a while back.
It doesn't actually "convert" the video per-se, but translates it on the fly using the codecs you have on your system. It's slower than reading the native file, but it will work.
http://www.iceinspace.com.au/forum/s...ad.php?t=24386
For what it's worth though, a WMV file is HIGHLY compressed, so the results you're going to get in registax are going to be pretty poor if I were to guess.
Turbo