What exactly happens when you upload the mod files to youtube?
Second try would be rename the extension to .mpg - MOD is JVC's stupid extension for MPEG-2 files. (Of course, do those tests on small uploads, lest they take a lot of time).
If all else fails, try VirtualDub (freeware) with the MPEG-2 plugin.
VirtualDub:
http://www.virtualdub.org
MPEG-2 plugin:
http://home.comcast.net/~fcchandler/...EG2/index.html
Open the file with VirtualDub. Click video, compression, and pick your favorite codec (some MPEG-4 version like Xvid or DivX is usually good). Click configure to adjust the settings to your liking. Then click file, save as AVI.