Yahoo has redesigned its Yahoo Video service (like previously reported) to allow user-submitted videos and to compete with YouTube. It allows you to tag videos, rate them, feature, and embed videos into your own site. Basically, it has got all the nuts and bolts that everyone else has. However, for Windows users the videos will come in windows media format and flash for Macs and Linux. This is a different move from YouTube but doesn't really do all that much to differentiate itself. The redesigned Yahoo Video will be popular mainly because it is Yahoo but I don't think it will dethrone YouTube.
Right now YouTube is like the holy grail of only video providers. YouTube is just so hot right now that I don't think Yahoo will make the dent it wants to.
If you wish to submit a video than it needs to be less than 100 MB and in wmv, flv, asf, qt, mov, mpg, or avi format.