How to resize and change DPI for digital photographs on an iMac?

I have an iMac computer and I need to have the capability of changing my digital photo's (camera-nikon d70) dpi to 300 and also resizing them to 4x6 and maintaining a high resolution. These requirements are mandatory, as they will be printed into the newspaper on may 17, and I need to upload onto the newspapers website by tomorrow at 10am. I have iPhoto, but I don't think I can do this on there? Should i download an adobe photoshop 30day trial? Or can I do this on the free downloaded program irfranview? Please give me as much advice, knowledge and detail as possible on this subject.

You've got it All WRONG! You do not have to resize digital images or change the DPI. In fact doing so without knowing what you are doing will end up with your image being rejected. What I suggest you do is make sure you give them the full size image as it came out of your camera. There's no need to change anything at all!

You need to read this before you even contemplate doing anything: THE MYTH OF DPI http://www.rideau-info.com/photos/mythdpi.html - especially read the section titled "The Horrible DPI Mistake". That's the one you don't want to make. There's also a section on how to resize digital images and change the PPI (not the DPI) properly without resampling the image. This is very important if you want to do it right without destroying the quality of your image.

There's no need for Adobe Photoshop. You should be able to do it in almost any raster image editor including the free image edtior GIMP http://www.gimp.org/...w.gimp.org - Mac version here: http://gimp.lisanet.de/Website/News/News.html

Hint: in GIMP you use File > Print Size, to change PPI without resampling.