I had been to RiteAid to take photo for DV. I had taken the print out of Photo information and photo size with me. They did not know what size is 600*600 px photo. They said they need actual size in inch and they take only 2"*2". I am also not good on this thing.

What should I do? Please your inputs.

If this is the case then have them take your 2"x2" picture covering your head to chest. Ask them to put the picture in CD.  Later on you can adjust the picture to 600px * 600px according to the DV requirement using photoshop.

Hope this helps.