Header image:
Move the shed (whole image) to the left a bit so that your text with the blurred background is not ontop of the shed at all. Also change file to .jpg
h3:
center them, add:
Code:
text-align: center;
in your css files where you refer to your h3 tags. It will center them over your 3 columns.
Footer:
sought it out, I'de put your xhtml, css and W3C buttons on the right hand side of the box where you have your second nav and and lose your second nav completely - its not needed as your pages dont extend very far. Ide then center everything else.
General:
I'de ad a slight fade to your green/olive background, going from dark to light (top to bottom) and add a fade to the olive that shows when you hover over your nav buttons - It just all seems a bit flat when I hover over them.
Obivously your going to sought out you gallery so I'll forget that for now! haha
Theres also no need to refer to your index.css file twice in you html code ;)
Other than that - I like it!
Nice work though - just a few final tweaks that are needed in my opinion.