HELP! I need help printing photos from Flickr

Okay, I am not sure if this is possible or not. My computer died about a month ago and I am going to be buying a new one in mid to late September. What I want is 4x6 prints of some photos on Flickr. Now, I am aware you can order prints on some (depending on if the user wants you to do that)When I went on the message board on Flickr they made it sound like the ONLY way you can have prints made is if you have the users okay.

However, if I see photo I like and it gives an option to click for various sizes (small, thumbnail,medium, large,etc)can't I make a print from that?

What I want to do is email the pictures I want prints of to either Walgreens, CVS, WAL-MART, or Target and have them use their photolab to make prints. I feel this is a rather easy thing that has become very difficult. I hate to wait til September, but if there is no other way I will. Any advice or suggestions would be helpful.

pictures from Flickr onto a disc at my local library? Once they are on a disc then take them to a photo lab.