A couple of months ago I sort of forked off a version of oggconvert and called it video2theora. Basically what I did was take the oggconverts projects glade file as a base and instead of using gstreamer I used ffmpeg to create a program that would allow converting video files to theora videos for use with the new firefox and opera video tags.
I hope this is only a temporary situation until gstreamer codecs on windows is in better shape. I attempted to get oggconvert to work on windows following the instructions on the website but gstreamer kept crashing. Hopefully this will improve in the future. Until then I will be using the gui based on ffmpeg.