Hey,
1.) You can modify the navigation menu to include an image relatively easily by editing the CSS for the menu items. The custom menu allows you to add a CSS class to the menu item link when you edit the item (if you don't see it, click on "Help" at the top right of the pae and check the CSS box) and add the class here.
For example, for the Home link you could use a class of "home". You would then need to add the appropriate CSS to either replace the text with an image or set a background, background positioning and padding to suit the link depending on how many you have and how large the image is.
2.) You can justify the text by adding this CSS:
text-align: justify;
to this code (style.css around line 207):
.nav li a strong {
display: block;
font-size: 14px;
font-weight: normal;
}`
James