[Gerben Zevenbergen]"wmv or another windows-format."
Any PC with QT Player should be able to read MP4 or H264 from your Mac.
You should be able to convert to those formats more or less fast.
Any more PC-friendly option (WMV, AVID) I think will be slower.
If you manage to get a hold on EPISODE (unfortunately not the cheapest), but man, that thing is faster than light - beats the crap out of compressor. Very good results in no time. And Raphael is right - do not convert to WMV - most PC users can read the QT files by now.