First of all this doesn't seem to complex to be using any child selectors, you really need to change behaviour for an element that belongs to different parents? and then it works in IE6 aswell. :)

descendant selectors works fine, also take note for specificity. selector selector2 vs selector#id selector. But this is simple enought so shouldn't be any problem right now :)

First of sort out all the different height definitions, #head = 150px, #logo = 160px(padding) and #header = 200px as floats don't take up any space.

No need for a clearing div as your main content is in a wrapper, clear the floats there.

Use good names :) left right center etc doesn't really mean anything. You can also import other stylesheets in another stylesheet document like @import url("style.css"); (depending on how you import it there is various support for old browsers, so importing styles like this you exlude browser that don't fully support css2 anyways) remember though that it has to be before anything else in that document except comments.

And to easy up some coding bugs, try to use padding on parent elements instead of margings, that will save you a shitloads with the double margin bugs in IE6 :D

Got a bit off-topic with random rambling but, look over your height definitions or make the parent autoclear(hint: floats clear floats, or use a hack for it ) or clear it inside where the floats are.

Cheers hjalmar