JPG files not opening on MAC

Hi Guys,

I went for a trip in the last month where I clicked a lot of pics. I initially transferred them to my windows laptop (JPG). After that, I transferred them to mac and when I view the same files in mac the pictures apear to be in .jpg.xml format (How is that possible?). Anyway, i converted them to JPG and still applications (preview and iPhoto) give me error in mac. I initially tried to open it from external hd itself and then even tried copying it on the desktop. But nothing happens. I was of the view that we can open jpg in mac and if i am unable to do so its going to be a big pain for me.

P.S I am new to Mac so I need your assistance with the same.

Thanks. Usama