Thanks for the tip Ronin 
, I just recently got my hands on an older version of Photoshop Elements so I'm still in the beginning of learning the features (previously I had a 13 year old beta version of Paint Shop Pro), any particular reason you'd go with horizontal over vertical for the grain? Guessing it might be that was the way photos were taken / processed back then so it caused horizontal grain but I am genuinely curious .
Photographic film is coated with an emulsion containing light-sensitive silver halide salts, it is these crystals that are the grain. In 35mm (most commonly shot film in use today) the grain is usually fine enough to the point where one can not see the actual grain pattern even after reasonable enlargement but it is there. On most film the grain runs from end to end the long way when it's manufacturered, It's very rare for film grain to run across the short way, I've only seen it a few times and all have been in large format films. In standard 35mm SLR's (and subsequently digital SLR's) the field is oriented slightly longer side to side to optimize the film useage, my Canon EF has a frame of 24 x 36 mm for example. That said the grain will naturally flow horizontally under natural orientation and up and down under portrait orientation. I like to remember it as "The grain flows the way the film travels through the camera."
Additionally, I am also aware of the shortcomings in photoshops grain emulation filter. There are unnatural gaps in the grain patern with the filter, these gaps are easier to conceal in the composition of the photo by running it horizontally.
