Some other options/things you might need to know ...

1. Floats are essential if you want a footer on a page that falls below the other divs. You have seen one discussion of floats from Minz Meyer that you could add a footer to; here is another from a workshop I was at, and here is a position: other one I did); It uses wrapper <div>s, IR, links styled as lists, and extra hover effects. There is also a CSS file that undoes most browser defaults.
2. To serve different CSS to IE 8 and below, and Firefox, the most usable techniques involve advanced selectors and pseudo-classes that are a part of CSS 2.1. See Zeldman Chapter 12.
3. To get the idea from point 3, here are Eric Meyer pages on
   Universal selector
   Child selector
   Adjacent sibling selector
   New pseudoclasses
   Attribute selectors
   Other than the Universal selector and the pseudoclasses, these are all things that old IE does not support (e.g. html>body ul{}, or ul>li+li {} or a[href="http://www.cnn.com"]> {}.
   
   But only old IE understands the Universal selector if it's placed before the html selector (as in * html {}). This shouldn't make sense, but IE thinks it does. It's called the Star HTML Bug and so it gets used to serve CSS to IE lte (less than or equal to) 6 , both Mac and IE.
   
   Finally, remember the conditional comments that also work only in IE. These are pretty powerful. You can use programming syntax: <!-- [if lte IE 9]>
   <link type="text/css" href="ie6_styles.css" />
   <![endif]-->
   
4. CSS comments as you probably know are like C++ comments:
   /* commented stuff goes here and can be multiple lines so that this example is OK */