I'm not familiar with macs...*cough* Not many free/good image editing softwares for macs (well, at least infranview and photofiltre dont work), but but but...
...The GIMP. Download the Mac OS version of that thing, and just flip through the menus until you find something that says something along the lines of, "Resize, Crop, Image Size, etc etc"
You may also have to crop your image so that the aspect ratio of the image is 4:3. Your camera may take a wierd length:height ratio like 1:1, which if you only resized to 1600px wide, your image will also be 1600px tall...thus you cant upload the image....(actually you could, but you would have to resize the image to 1200px tall, which would leave 300px on each side of the image to fill with black space...but dont worry about that for now).
Just make sure when you upload, the size is 1600x1200px (pixels), 1280x1024px...etc etc.
ok, so I'm not thegreatest at replies and comments. Sorry. For anyone needing to contact me, my email is back up inmy profile. >> my cluttered mess of a gallery <<
Just checking....I assume you do not have either Adobe Photoshop or Adobe Photoshop Elements installed on your computer - - ? Both are available for MAC, though, if you don't have them, they are not freeware. Photoshop is quite spendy. Photoshop Elements costs considerably less. Both will resize pictures, among a wide variety of other things. Wen
you could always just use iPhoto - the image editing app that comes bundled with iLife on macs - as far as I know you can crop, resize, edit colour, sharpness etc all with that.