Its all to do with image ratios, your camera will take a shot and the the hight to width ratio of the image in your camera will be set (for example 6:4)
You then go to boots or where ever and ask for your print on 7 inch by 5 inch paper (ie at a ratio of 7:5)
There is obviously a discrepency between the two ratios, so
to carry out this request rescaling has to happen and as a result an amount of cropping occurs and you loose some of the image detail, or less commonly you end up with a blank border along one side of the print.
The solution is to not frame your digital images too closley leave a little room around the subject. Then using a editing program such as photoshop or nikon view you can resize/crop your image at the ratio that you will ultimatley print at.
ie, you tell photoshop "i want to print this at 7x5" it then gives you a tool to crop and frame and compose the picture how you want it while keeping the ratio true to your print size.
If that sounds like too much hassle then you could always try a number of different print sizes and through trial and error discover which is closest to your cameras recorded ratio and gives least loss of image - then always get your prints done to that size. 9x6 and 6x4 are generally the closest match in my experience but I guess it depends on your camera.
hope that makes sence and hope it helps
