Title and Tagline Overlay Shifted 70px to the right on IE6 vs IE8

I have used Overlay Blog TITLE over Header Image(s) and Overlay Blog TAGLINE over Header Image(s). I also put margin-top: 20px; and margin-left: 140px;. It looked nice on my home computer with IE8. When I got to a different computer with IE6, Title and Tagline appeared shifted to the right some 70px overlapping with some image details. Vertically, it was fine. I was able to put it back by changing to margin-left: 70px;. Now it doesn't look good on IE8 - it is shifted left.

My question is why IE8 and IE6 interpret the same setting differently. I can sure upgrade IE6, but it won't fix for some other people out there who happen to use IE6. Is there any other setting that can enforce the position of overlay a little more transparent to the web browser version? Thanks.