You must be running the verison of UDK optimised for Rift. Downlaod it from the Oculus Rift developer site.
Start your game in PC mode – from editor – then press F11 to go fullscreen. If its not already stereo and warped then:
Hit Tilde ’~’ to open the console, type stereo on, hit RETURN then type HMDwarp on RETURN.
There are also a bunch of config tweaks that improve the look of it and disable some stiff that the Rift doesn’t support. I will add these here later.
Other stuff. I noticed that when I have my wireless xbox controller usb power supply plugged into laptop RIFT didn’t like it. I am using a USB power cable not the standard RIFT one. Its a 5v 1000mA USB to M-type connector. You can get from Amazon, its made by StarTech http://www.amazon.com/StarTech-com-USB2TYPEM-Barrel-Power-Cable/dp/B003MQO96U