Well the picture will be cropped no matter where you go since the format of digital cameras does not match the format of prints. The only way to aviod this is to crop to the print size you're going to print before you go to the store. Also, the in-store kiosks do an auto correction, which you can turn off by unchecking the box at the bottom center of the screen when you're ordering. Though keep in mind your screen is likely not calibrated to the printer anyway. I worked at walmart 5 years as a lab manager and can say that 99% of the time the image on the screen will match the print. IF you're using the Kodak kiosk, stop, they suck no matter what.
If you don't mind paying a bit more use Mpix.com they will professionally color correct for you before printing - though cropping is still done unless you fix it before hand since there's no way to avoid it. 4x6's are $.29 though, but it's worth it.
If you don't mind paying a bit more use Mpix.com they will professionally color correct for you before printing - though cropping is still done unless you fix it before hand since there's no way to avoid it. 4x6's are $.29 though, but it's worth it.