My theme looks like dissaster in CSS in IE6 and IE7

It seems much more to me a Tag missing issues in HTML, or CSS padding or margin issues.

Hard to tell without seeing any code, but it looks like a typical margin/padding issue having to do with your floated divs.

It could have to do with IE's broken box model.

One fix that sometimes works for these kinds of problems is to make sure that you never define width/height and margin/padding to one div - instead you should use two nested divs and assign width/height to the outter div and margin-padding to the inner div.

Another possible cause is the fact that all the browsers use a different default stylesheet, which means that if you don't specify (override) the margin/padding for all your elements then the browser will do it for you. You could try making sure you have all padding/margins for all your layout elements set. This means that if you want zero margin for an element then instead of just leaving it blank (which basically says you want to browser to decide for you), you would enter "margin: 0;"

Another tact that some people take is to use a universal selector to clear all padding/margins at the beginning of your css, which essentially wipes out all the default padding/margins defined by the default browser stylesheet. It looks like this: "* {margin:0;padding:0;}" This works well but then you are stuck with the task of defining all these default values (such as the default margins for p, h1, h2, etc.) yourself and results in more css.

Once again - hard to say without code to look at. Good luck!