If you are buying photos you should consider how much of the photo you are going to use and whether you would need to perhaps zoom into a particular part of the photo. Even then you are probably not going to need a huge 300dpi shot.

You can usually get a shot that's around 500 to 700 pixels in size, which allows for all of the above and then to export at 96dpi. Xara Xtreme exports JPGs at 96dpi by default.