Look for freeware to convert mp4 to window movie maker format.

http://www.videohelp.com/tools/GSpot should be useful in identifying the codecs involved in the video. Once you know what you have, you can install those, then use tools like VirtualDub (http://www.virtualdub.org/).

I've just realised you could do this with iTunes (I know it works on the Mac side and I presume the same options are available for windows.
If you bring a copy of the video footage into itunes, you can use the Get Info command on the video (right clicking) and set the start point and the end point of the section you want. Then you can right click on the video and choose convert to ipod format. This will create a new video of just the selected parts of the original. Drag the new video from the iTunes window to where on the computer you want to keep it, and upload to youtube or whatever.
Reset the start and stop times on the original footage, delete the new video from iTunes, and you are ready to repeat the process for making other excerpts.

if all else fails, you can ask here

Found the freeware. It's mp4cam2avi. http://www.brothersoft.com/mp4cam2avi-download-134631.html

Works like a charm.