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: 
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.
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.