I have a build thread in RC Scale I want to add a "walk-around" and "First flight" video too. I've searched all over and can't find the answer. Can I add the two videos directly to the thread as thumbnails, or how do I do get a video in the thread?

you need to upload the video to you tube, RCUniverse video, or other video upload site, then insert a link on your thread.
http://www.rcuniverse.com/mvp/mvpPosts.cfm
there isn't a way to directly insert a video into your thread.