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?
My first thought when reading your post was to adjust the line-height, but since you've already done that, I'm not sure how much more can be done. From your summary, I gather that the design cannot be modified to account for the large font sizes.

Another answerer recommended using pixel sizes, but I would recommend using ems as they are percentage dimensions and will be more consistent across browsers, screens, and resolutions.

Line-height can be left as 0 (or set it to the height of the parent element), but you will likely see the text floating over other elements if the text's height surpasses the line-height.

Any possible way you could use an image for the text instead? That's really the only fool-proof method for getting all browsers to look consistent.