The downloading of tables won't be noticeably longer for most webpages, they would have to be very long and downloaded on dial-up for any difference to be seen.
Floats for elements like divs, images and other elements gives much greater flexibility, it means elements can be put in very different positions instead of just having one cell on top of another or having lots of stacked or nested tables, so it creates neater, shorter code but it can be difficult to get them to do what you want. There is also a much greater variety of margins, padding, borders, etc. for each or any side of an element which is easier to control with CSS than with old table coding.
If something stays where it is on the screen while you scroll, so that the other content moves past it, then it probably has position: fixed which IE6 and older browsers don't support. If it moves down the page while you are not scrolling or doing anything, then it could be a flash image.
Use an online tutorial like:-
http://www.w3schools.com/ (very detailed)
or
http://www.wickham43.supanet.com/tut...roduction.html (an introduction).
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.