That's great... Looks good.
I have a question... If you put fixed at the end of your background line in ATO>Body, Text, & Links like the code below only the center column will scroll. I often like that effect for better readability but would like to get other's oppinions. Would you mind trying that and let me know what you think?
background: #aaaaaa url("http://hvmac.dreamhosters.com/wp-content/themes/atahualpa/images/background.jpg") repeat-y center center fixed;
You should be able to just paste this code in place of what is there but copy the current code somewhere in case you don't like the effect.