Using blender to render 3D text in an existing movie

Hi, I’m new here. I have been researching this a bit and I am stumbling. I am able to add a video as a world texture but when I render it is splitting the video in the middle, like the left half of the video is showing on the right and the right half of the video is showing on the left. Also the quality seems off. I’ve watched a few tutorials on youtube and when they are adding the video as the world texture and then adding influence to the horizon it just shows up and it’s lined up perfectly and scaled perfectly. All I really want to be able to do is render 3d objects (just text right now) inside a movie that I’ve recorded using a desktop recording software. I want to preserve the original movie as it was recorded and just want to superimpose the objects on top of it. Is there a good tutorial for this anywhere? Thanks!

you can add the footage in the VSE or compositor
tutorials:
http://www.blenderguru.com/videos/introduction-to-the-compositor
http://blendernerd.com/cg-overlay-on-video/