How your head is structured depends on what you want to include and what you actually need to include for a given doctype. An example:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
<html xmlns="click here" xml:lang="en" lang="en">
<title>Title of page goes here</title>
<meta http-equiv="Content-Style-Type" content="text/css" />
<link rel="stylesheet" type="text/css" href="index.css" />
Note the absence of the <?xml version tag above the doctype. I leave this out to prevent IE from running in quirks mode.
It would be a lot easier to assess if you post your head as above.