Whats good Sitepointers?
I have a large, old, and rather complex site that I've inherited which I'm slowly working on renovating. I've made some fairly dramatic CSS and HTML changes to the UI - which need to work in all modern browsers *plus* IE 7-9.

In using IE Web Dev Tools (in IE10) I'd like to get some input on the best way to test for older versions of IE, and the Browser Mode and Document Modes are a bit confusing. What is the best way, or combination of Browser & Document Modes to test for each version of IE?

Here is the current Doctype and meta info:

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">

<meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta http-equiv="content-type" content="text/html; charset=iso-8859-1" />
Different combinations of browser and doc modes render differently. What is the best combination to use for each version of IE with the code snippet above?