Use a plain text editor, I recommend the free TextWrangler (http://www.barebones.com/products/textwrangler/) but others may have different preferences.
Generate the page in iWeb, then open the html files in TextWrangler to make adjustments, add code snippets, etc. Then when you're comfortable with html, ditch iWeb and start coding on your own:
<?xml version="1.0" encoding="utf-8"?>
<!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" xml:lang="en" lang="en">
<head>
<title>An XHTML 1.0 Transitional template</title>
<meta http-equiv="content-type" content="text/html;charset=utf-8" />
<meta http-equiv="Content-Style-Type" content="text/css" />
<style type="text/css">
body {
color: #333;
background: #eee;
}
</style>
</head>
<body>
<p>Your HTML content here</p>
<p align="right"><a href="http://validator.w3.org/check?uri=referer" target="_blank">Validate page</a></p>
</body>
</html>
;)
