How Do I Merge a Before and After Video Together In Sony Vegas? (Read More)?

This is really hard to put into words in the title. But basically, I have two videos, one is a video before editing and changing the colour of the video and the second video is after changing the video settings and colour. So, with these two videos of before and after, I want to be able to merge them together so that the entire video fills the screen but with one half being before and the other half as after. When i search this in google i find things that show me how to put the two seperate videos side by side on one screen, but I want them put together so it's half and half. Watch this video to see what I mean, it's just an example, i want it like the picture at 0:06, http://www.youtube.com/watch?v=GB6dWQZxj34