I would like to use this photo of a fountain pen in my new business
letterhead.  My printer says the file must be 600-dpi.  1] How do I
obtain this?  2] What is the cost?

Thank you.

http://images.google.com/images?q=photos+fountain+pen&hl=en&lr=&start=80&sa=N

Image is 3rd row/ far right/ fountain pen/ writing on paper

Isn't the name Iridium the name of a sattelite?

The image you describe is copyrighted material.  Try registering on
the worth1000.com site and getting in contact with the owner of the
picture (his/her info is on the site).  He/she will most likely be
able to get you the picture at 600 dpi.  Cost is up to the owner.

The image with a link to the owners info is found on:
http://www.worth1000.com/emailthis.asp?entry=66710

If you are open to other high-quality (300-600 dpi) images of high-end
fountain pens, I suggest you go to www.corbis.com and type "fountain
pen" into the search screen.  Make sure you check the box next to
Royalty Free and UNCHECK the box next to rights managed.  Often, these
images are relatively inexpensive. The least I've spent on Corbis was
$79, the most was $1300. Also, your printer should be able to work
with a 300 dpi image. He's going to print it at 133 line screen. 
Double check with him, but I believe that, at full size, he should be
able to work with 300 dpi with no problem. The 600 dpi would be if he
had to work from a small image and enlarge it without losing quality.
The images on Corbis have relatively large dimensions.  Good luck!