i don't quite get ur question.
ok.. say u ahve a photo opened, and it's already in 3:2 format. and u wanna add more space around the edges of the photograph so u can add ur border.
you have to go to image ---> canvas size, and type in the same percentage for both the height and width (select the percent option from the drop down menu). make sure that ur image isn't flattened (there will be a padlock and the layer name will be in italics, to unflatten it, double click on the layer and rename it, i usually hit enter and use the default name) when u do this otherwise the extra area created around the photo will be filled with the background colour, and be merged with your image on the same layer. doing this will resize with the same ratio.
alternatively, you could specify your own size. say u have an image at 1800x1200. and u want a white border that is 20 pixels all the way around. but if u add 20 pixels to each side (ie, 1840 x 1240) the image will NOT be 3:2 anymore. u will have to crop ur image accordingly. so to end up with 1800x1200 with a 20 pixel border, u need an image that is 1760x1160. i think u already know how to get an image exactly that size rite?
after u get that size, u can go ahead and make the canvas at 1800x1200 anchor in the centre, there will be a border around the edge of the photo at 20 pixels all round.
kaoz.. i dunno if i've confused u further. i must really suck at explaining. showing u is best! hahah can show u in 2 mins. :think: :what: