Hi thejoebenn,
Yes, you can use it in portrait. It won't void your warranty. Anything else I can help you with?
HD Tech
I want to use a TV in portrait orientation to show full screen images & videos.
Some screens are not warrenteed for use in this orientation, is this ok for Samsung TVs?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic