I use Firefox and IE, and the difference I see is sometimes things get overlapped in one browsr, while they're perfectly fine in the other, and it's always either one of them..
Have you tried putting the images into a table in the way you want it (1 row, 4 columns, no border, no cellspacing or cellpadding) to see how it looks in both? That might be an alternative instead of having problems like that.
Make each row of seperate lined up images into a whole image. You know, copy and paste them and position in Paint. Then, all you have to do is upload it and center it on your lookup.