Help with video size reduction?

[Super Firebug]

I've been trying to find a way to reduce the sizes of several MP4 video files. If I'm wanting to reduce MP3 audio files, for instance, I can load them ino Audacity and re-save them at a lower bitrate (at a loss of quality, of course). Is there a method (preferably free) for MP4 video? The videos are of people giving addresses, speeches, etc., so quality loss isn't as big of a deal as it might be with movies or whatever. Thanks for any help.

[Pengy]

You could try Avidemux.

[The Fifth Horseman]

I'm using VirtualDub. Initially setting up everything (this was specifically for MKV demuxing and transcoding into MP4) was a PITA, but it's prety easy after that.