Ummm.... there are only probably about a thousand places online where you can send the file and have it printed. 5 x 7 is NOT a big print. Or, as you said, you can put the file on CD or a thumb drive and take it to Walgreens or a similar place to be printed.
If you want to do it on line, Mpix is as good as they come.
http://www.mpix.com
Keep in mind, no matter where you try to have it printed, you need a decent quality and high resolution photo to start with. No tiny, low res photo you have pulled off the internet somewhere, and also most cell phone photos print very poorly.
steve