To edit it? Well, it wouldn't be very fast, and you'd have to know exactly what you're doing, bit for bit (almost literally). Assuming that you don't know the format and you have no tools that can make up for that, that option is out.
I know for a fact that two videos can be sent at once with Windows Media Player (if you ever look at ifilm.com, they send an ad before each film). You may want to look into their HTML code, I'm sure it will at least help you move foward.
