positioniseverything.net is your friend. Since I left this world a long time ago (thank God!), I do not envy you, but the problem usually is double filling, especially. if your popups do not line up ("dropping").
You can crack IE6 with width:30px; _width: 20px; width:30px; _width: 20px; in your stylesheet, where in rule _ at the end is the IE6 setting that you want to do. This works for all rules in all directions.
But every time I had a problem, it usually was up to double filling horizontally, which really delayed floating divs in IE6.
Good luck. As I said, I do not envy you at all. IE6 is a plague that needs to be eradicated.
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