Create the frame, right click and choose the appropriate fitting options and then place the image into the frame by using the file>place command and hovering the mouse over the frame before clicking.
I think I might do this a little differently from Bob (though I would definitely Place, not paste, the image -- you only get the low resolution screen preview when you paste raster content, and you can't edit it later). Instead of drawing the frame first, I would simply place the image. In CS4 and later, when you place an image, if you hold down the mouse button and drag, your image will scale proportionally as you change the size of the frame you are drawing, so watch the smart cursor numbers and drag to 112 mm width. Now select the frame, click the center point in the transformation proxy, and type +8mm after whatever is listed in the the height and width fields in the control panel and press enter.