You want to make your action in image ready not photoshop. Image ready has the File > place command, where you can specify the distance from edges of the image. (photoshop has the place command, but in 7, it only works on vector files)
Can you do a - paste - flatten layers - save (over original) batch? Your images would all have to be the same relative size for that to work. Ideally you'd want to paste the entire layer and not just the text bit. As photoshop would paste it directly in the center of the image... or nowhere near where you'd want the text…