I don't know how kinko's works but most printers I know of have Photoshop and can size an image to whatever size you like. It's important that you render it to a very high resolution so your image is not pixelated or suffers from aliasing. Some say around 4000x4000 pixels is good, maybe less if your prints won't be very large. One thing you may find is that your colors don't match what the printer prints. It's therefore a good idea to get a small 'proof' of the image to compare to what's on your screen. If they're not the same, or close enough, then you have some work to do. First is to calibrate your display setup. There are lots of sites that have information on this procedure. Photoshop has a quick and easy program you can install called Adobe Gamma that works pretty good. Let us know how it goes.

Cheers,

Tim