Try not using absolute/relative positioning, but using floats instead. Much easier and less likely to fall apart x-browser.

I've found in the past that a lot of the cross-browser problem stem from the varying 'default' CSS values applied by each browser. This is most commonly seen in margins and padding (IE already has a poor interpretation of the 'box' model) If you set the margin and padding to zero for problem elements and then set them again, the browser is forced to honour the style sheet values, resulting in a more consitent layout across browsers.