I have a 10 x 100 px image which I want to tile horizontally in photoshop (not using css). Is it possible to do this in photoshop?
Yes. In Photoshop: You use "Command A" on Macintosh or "control A" on Windows to select the entire 100 x 10 image. Then while selected you select "define patern" Then you change the "canvas size" to the desired new size and select edit/fill/pattern/ your pattern.
I made a video on this a little while back try this: http://bit.ly/baX1M5 (@danramosd me on twitter if you have anymore questions)