Absolute positioning can be problematical across browserland, and is best used only for a small occasional element inside another div, since overlapping and other undesirable behavior can result with absolute positioning from the client resizing the browser window. It's best to eventually get a handle on using floats, which are better cross-browser. I offer you my online
web development bookmarks, where lots of info can be found on layouts, bug busting, css tricks, and other things of interest for those learning how to hand code.
One hint I'll give you- ems are great but do NOT use them to set font size on body or you'll trigger font sizing bugs in more than one browser! Set the font size on body to be 100.01% and then adjust using either percentage or em for your inside elements (I usually use the main wrapper for this.)
I love developing with xhtml/css! Feel free to contact me if you have a specific question.