You can use iPhoto to resize images using the "export" function. It's crude but serviceable.
A better alternative is the Gimp for Mac.
http://www.gimp.org/macintosh/
It's an open source version of PhotoShop. You have to have X11 installed to use it but it works
very well.
(If your mac doesn't have X11 installed already X11 can be installed from the Mac installer disks.)
Btw, beautiful pistol.
I never see anything like that even remotely realistically priced at the shows around here.