Jon there may be other problems, but the glaring one is
HTML Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
You can't declare the DOCTYPE twice! And you are opening <html> again. Both of these things are probably already located in /customer/home.tpl
Dynamic drive's instructions could certainly be improved on this one. Menu looks nice, worth the effort.