Question: The font size I need to match the design I have is 85pt, which is extremely large. In IE6 and IE7, my design is affected because the divs that contain these elements become larger than they normally are, and as a result, elements under these are pushed further down, somewhat breaking the design. I have the height defined for these elements and when I decrease the font size, the elements begin to shrink to the correct size. I've added line-height: 0; to the element and this works in all modern browsers.

Unfortunately, the design I'm working on cannot be shown publicly, but I was hoping to get some insight into other possible techniques that I could try to get the design to render correctly. The height of the parent element is 144px, which includes 10px padding on top and bottom and a top and bottom 1px border.

Unfortunately there's not a lot more that I can add to this, but I'll include whatever info I can if asked.

Answer: 
line-height:0 is a great start. However, I'm a little concerned about the 10px padding on the parent element. Whenever you mix padding with IE, you start to lose control over width & height.

I'd start by removing the padding-top on the parent and convert that into a margin-top:10px on the actual child element. If that still gives you trouble, remove the margin and try a position:relative on the child with a top:10px.

Finally, try adding a overflow:hidden to your parent element to force it to not budge when the font-size gets larger.

All this depends on what your child element actually is. If you convert it to an inline element (like a span, em, or strong) it might help alleviate some rendering issues, depending on your predefined styles.

Another thing to consider - are you using floats? Sometimes you'll get a double-float issue with IE and floats. A quick google for "IE double float" will show you why.

Does that help?
Convert the font-sizes to pixels and use px instead of pt. Make sure there that padding, margin and border is 0. Verify that there are no whitespace in your HTML except for between words. Whitespace can end up being displayed as a newline or space, making elements bigger than intended. Also don't set line-height to 0, set it to either auto or the same as font-size.