do you absolutely need to use relative sizes? hard-setting the size might make life easier. try this:
20% both ways is 128x96
35% both ways is 224x168
the dimensions you have set should make 224x96
IE does all relative sizes based on the table tags just outside the assigned item, so if you make something 10% inside a cell, it
will be 10% of the cell, not the page.
I do all of my developement for IE, so i know it's guts pretty well.
Feel free to look at the behind code in my galleries (
http://scaredyet.net/gallery/ ), i use the exact same technique