How do you create a "side scrolling" effect?

I'm trying to make a wad in GZDoom, but an intergral part of the wad relies on creating a side scrolling effect: basically a camera that mimics the player's moves. How would you go about creating this effect?

Anyone? I haven't the foggiest idea where to look on the ZDoom Wiki. :(

Ask the guy who made this. I think he goes by TheMisterCat.
http://www.youtube.com/watch?v=cRVV7gPD_ho