You will need to create your graphic design into a DotNetNuke skin. I roughly this order, you will need to:
- Chop up the image in your graphics design
- Add in navigation
- Add in panes
- Create CSS to put images in the appropriate places
- Create CSS for styling the panes and navigation
You'll undoubtedly benefit from looking at the skinning tutorials listed
here. Pay special attention to the skins at the bottom of the page. By seeing how those skins were created, you should see how to create your skin.